Makes sure Bolivar lives a little longer to crush the caudillos and I'd imagine the best hope is a centralised, bureaucratic junta government to keep together long enough for the glue to settle, there'd probably be a decentralising/conservative backlash at some point but a generation of stability will ensure the pretty thin lines of national difference don't take root, beyond regional tensions ala the Italian Northern League of nowadays, or Bavarian autonomists.
Contrary to that I think that a better PoD would be removing Bolivar from the scene or, at least, changing considerably his (specially late) thinking. My point is that the centralist-autonomist tensions, created in part by Bolivar's totalitarian and cetralist aims were the main cause of the Gran Colombia dissolution. Bolivar's plans went against the complex sociopolitical reality in the region. If they manage, like in Mexico, to find a point of balance where the different groups of interest can share the power peacefully, I think that Gran Colombia could survive.
Another thing is the "stability" in that surviving Gan Colombia. Depending what we call stabillity, maybe the country can have some sort of stability, but never like the idea of stability that we have in our XXIth century liberal democracies. Even in TTL there will not have a proper national market, national infrastructure, national army, national bureocracy or a national identity at least until the second half of XIXth century, being optimistic, at least without a PoD in the colonial times. We could say that we are speaking about an ancien régime state disguised in liberal republic by paper laws. But at least in TTL they don't switch the spanish king for Bolivar.
Regarding the effects in the world, these are my suggestions: I think that probably the XIXth century would be pretty similar to OTL. Probably they avoid the external debt problems that had Venezuela in the late XIXth century and (shameful) historical figures like Cipriano Castro. That means not anglo-german intervention an less tensions between the USA and those countries about the Monroe doctrine that could, in the case of Germany, butterfly some things in the Great War. Perú would have some troubles in the northern border, because is not the same thing confronting Ecuador than confronting a united Gran Colombia. It's in the XXth century when Great Colombia could have more impact. I think that they could keep Panamá, with or without canal. That opens a new possibility: If the great powers don't see Panamá as a future booty because there is a stronger Colombia, maybe the canal is made in other place,
perhaps Nicaragua.
With the oil reserves and the coast in the two oceans, they could be truly competing with Brazil for the leadership in South America to our current times, and become a comercial and economical hub in the continent.
And last but not least, a García Márquez from Gran Colombia could be amazing.
Cheers.