I've voted yes, because once established - I think such states would be more viable.
The difficulties are establishing who would rule the new states, and motivation. Now admittedly, this wasn't an issue with invading the Levant, the crusaders agreed on a king, and there was the prestige of ruling the holy land. The Pope will need to make a big noise to encourage N.African crusading - mentioning pilgrims, relics, and bigging up Carthage as rightfully Catholic land could certainly help - you aren't going to do much more than @LSCatilina suggests without that motivation.
NOTE : Everything after this point is splashed with optimism.
If you do however .... a North African crusade would lead to either one very large kingdom, or two smaller ones (my preference). It'll take a while to establish any lasting power, but with some Papal subsidies, and a Holy Order or two (i.e. The Knights of Tangiers, and the Knights of Carthage) to back them up - they could rebuild, and start converting (as best they could) reasonably quickly. We're just concerned now with how receptive the rulers would be to Berberization or Magrebization and how effective conversions would be, otherwise we risk a barely less precarious Jerusalem. I'd expect a Berbo-Iberian merger culture to be the result of the melting pot. Though sadly, it'll make next to no difference to pirating in the med as the Barbary pirates haven't emerged yet.
If successful, the Kingdom of Mauretania would be a shoe-in for competing with Portugal and Spain for new world colonies (butterflies winning), and certainly help benefit europe discover the wonders of inflation due to access to both West African gold, and new World gold!
The Kingdom of Carthage/Tunis would likely be the home of the most eager crusaders, as it is nearest the next (ATL) logical target - Cyrenaica/Cyrene. A tiny prize that would most likely become a Holy Order (you couldn't exactly form a Kingdom, it isn't exactly bursting with wealth, and as such isn't that tempting) - which makes any potential Levantine crusades, or Egyptian crusades outstandingly practical, as there are now two coastal routes - Cyrene, and Byzantium.
How long-term viable could these states be -
http://en.wikipedia.org/wiki/Christianity_in_Africa#After_the_Arab_conquest
There seems to be evidence of Christian communities during the period of the potential crusades, and pilgrims could certainly be charged taxes - which would make Italy, Carthage, and potentially the Spains and Mauretania a good helping of income. Plus, without the religious animosity, Genoa could certainly help facilitate a vast increase in trade in the Western Med, which whilst there would be piracy, would help the fledgling states.
Plus, both states have good defences against any major threats - with the exception of nomadic Berbers, the nearest muslim states are in West Africa (if they have emerged yet), or across Libya and the Fezzan - which kept Ancient Carthage safe from Egypt for centuries - a new Carthage backed by chunks of Europe will be much more likely to be prepared for a muslim invasion across the desert - which is difficult by anybodies definition.
An interesting facet would be crusading Berbers, and Desert Crusaders - after learning in N.Africa, you could see troops less constrained to water as happened in OTL, and more lightly armoured, who would provide a crucial balance to the forces that were used in crusading IOTL, and being fluent in Arabic, could help make an ATL Jerusalem more stable, if the muslim world isn't strong enough to defend itself.
The last interesting thought, I apologise for being off topic - is that the success of the Catholics could lead to a very isolated Orthodox church, as I'd expect all the newly instated Patriarchs would be willing to kow-tow to the Pope in Rome a bit, at least in the short term - which could lead to the Romans being shamed into ending the Schism of Catholic terms.