they were big and important until the 1820s ... then the started a very steady decline until teh growth of Washington, DC during the New Deal. the scramble for Africa occurred after VA's heyday. This is also why presidents form VA abruptly stopped pre-Civil War.
True, but a big part of what sapped Virginia's strength was the rise of the industrialized north, it's alignment with the slave-owning south, and how most immigrants moved to the North and West, and many of Virginia's best and brightest moved elsewhere.
With the USA out of the picture, it's a whole new ball game. Virginia would be in a position to be the dominant power of the region. As mentioned before, they own OTL Virginia, West Virginia and Kentucky from the outset, have a strong chance of absorbing most of OTL Tennessee, Indiana and Illinois, and maybe even absorbing Maryland/Delaware and North Carolina, or at least parts of those three. Toss in being the only one of the 13 Colonies to be in a position to claim land on the west bank of the Mississippi, and they have the best position on paper bar none.
This is doubled by the fact that they have strong leadership (Jefferson, Madison, Henry, Clay, Houston and the like), plenty of land to attract immigrants, resources and capitol to industrialize, and maybe even abolish slavery from the outset given how much the early Virginian statesmen favored abolition. The Old Dominion would do well indeed!
As far as colonial U.S. states: One thing to consider is whether or not some groups would eventually form smaller c(con)federations. there is no reason to believe that New England and NY might not draw together given their shared merchant/industrial character and the need to fend off continued British presence in Canada and possible conflict with other states with conflicting interests and clamis in North America. As a result, the New York/New England Yankee Confederation might focus on merchant marine and industry and seek to carev a piece of Africa and/or the Caribbean off as raw material suppliers.
Since the south remained largely agrarian, I don't think they would have the means or need to become colonialists. Think about it: they do not develop much industry even into the early 20th century, what need have they or raw materials? They are raw material suppliers to Europe and the North.
You have a point about regional coalitions.
I see Georgia and South Carolina banding together out of necessity. They might rope in North Carolina, or lacking that, divide it with Virginia. Give them time, and much of Alabama/Missisippi will be under their control. Reliant on cotton and slave-based agriculture, the most backwards and underdeveloped of the former British Colonies.
North Carolina will certainly join or be divided by a stronger neighbor. Only Question is if that neighbor is Virginia or the Georgia/S.Carolina confederation.
Maryland might try to make a go on it's own for a while, but I see the lure of federating with one of it's neighbors being too strong. My money would be with Virginia, seeing as the combined power would make the Chesapeake Bay their own personal little inlet.
Delaware is screwed. Only question is who annexes it first, Maryland or Pennsylvania.
Pennsylvania, New York and New Jersey are the wild cards, the former two especially. New Jersey will likely be New York/Pennsylvania's Maryland - makes a go at independence before merging with a larger neighbor for mutual benefit. Pennsylvania could be independent and prosperous on it's own, and in which case, it would likely serve as the region's mediating power, given it's sole land claims would likely be in Ohio.
Of the bigger two, New York is a wild card especially. It could be a notable power on it's own, but it's an absolute game changer. It joins New England, the trade/industry and position of the region raises all the more higher. It joins Pennsylvania/New Jersey, the resulting nation would likely serve as the other great power of the region along with Virginia, taking form like a smaller, more federalized version of the OTL United States. They'd also be in a much better position to claim more territory out west and elsewhere - I could see them aim to make the Great Lakes the core of the nation, expanding into Ohio, Michigan, dividing Indiana/Illinois with Virginia, and snagging the remainder of the Northwest. As they develop and industrialize, which would make the stature of the nation all the greater, I could see them making moves for lower Ontario, or far more likely, seeing yo buy it from the British, which they might get, given Britain would likely want to play them off with Virginia.
New England is pretty much what we'd expect - a moderately industrialized, heavily mercantile gentleman's republic, like a region sized version of Nantucket. If they can rope in New York, they may make a play for greater expansion - otherwise, I see them mainly sticking to themselves, focused on trade and industry, though they may make overtures to absorbing Acadia when the British pull out in time. Oddly enough, New England is also the one I see most likely to set up colonies. Maybe a few islands here and there, starting as whaling stations or trading posts that grow into something more. If Belgium can get colonies, I certainly can see New England get some.
I severely doubt it. Filibusters worked only against areas that had a weak hold by the empires in question, and weren't worth the trouble in keeping anyway; the force of the UNITED States was behind such takeovers(even if it was in an unofficial capacity); and lastly, the presence of American settlers being there already.
As for Central America, there's a difference between already thoroughly populated states with mountainous and jungle filled terrain rebelling from an empire with internal problems than having numerous small rival states competing with said empire over territory. By the time the Anglo states managed to get enough military dominance over one another to safety expand beyond the Mississippi basin, they're going to most likely be dealing with a Mexico that has sorted its shit out. All it has to do is play them against each other and arm the Natives.
More than likely we're going to see Mexico and Britain using the independent Anglo states and Native tribes against each other in dominating the west. The Oregon territory is almost certainly going to be Britain's playground; you could make a case they might even scoop up California. There might be some small victories for the 13 (or whatever number remains after they fight it out), but they, as representatives of New York or Virginia or whatever, or trying to found independent states is so unlikely outside of luck, and very weird and specific scenarios it's almost not worth considering.
What you're proposing sounds more like those who believe the CSA is somehow going to transform into USA part II because of some residual USian super power pixie dust. The strength of the US is the United part of the name, allowing the country to expand relatively unopposed to the Pacific. This will not be the case without such a union.
This really depends if you think the loss of Northern Mexico had more to do with American Expansion or Mexican instability. If the former, you are right, if it's the latter, the lack of the United States wouldn't change a thing but which flag replaces the Eagle on a Cactus in TTL Austin and Sacramento. Hell, Northern Mexico might even break off for good TTL. I personally support the latter theory, and think Europe would be just as happy to divide and play the various smaller states of Mexico as they would America. One things for sure, the Continent would be a LOT more divided then OTL.