I tend to plan with a bit more involvement than simply “see IPCs, must take”. 🙂 The chief consideration for me is not the weight of one particular territory or its nationality, but the strategic situation taking it will create.
For instance, you mentioned the choice between taking Sinkiang and India. Sure, one is 2 American IPCs and the other 3 British and based on that consideration alone I should strike India, but look at where it will put my forces if I take Sink. Right smack under Russia. Sudenly the Russians will have a few more threatened territories and since I know they don’t usually have infantry to spare, if I have at least one armor in my force, I can blitz some of those IPCs. Even without armor, I can draw some of their forces out. If I have another force working up to Russia’s capital, that’ll be a nice help for them. If I don’t, presumably Germany does.
India, on the other hand is a nice choice because it will open the way to mideast territories that are usually ill-protected. It may make strategic sense to take if it is not too heavily defended. If it is, an attack there will be diverting a large force into a very bad position where it will have nothing to do for the next 1-3 turns.
In Africa, I don’t see how it matters that much if you hit UK or US territories. Both of them are overseas, so those IPCs would arrive on transports exactly one turn after being built anyway. So, when I do look at nationality, I mostly differentiate between Soviet and non-Soviet.