This is exactly why I still have my PSP for now.
The US store is much better stocked for PS1 goodness than our crappy UK store. Titles like Dino Crisis 1/2, Spyro trilogy, complete Final Fantasy collection etc are all there. They also have a treasure trove of rare RPG's including classics such as Crono Trigger/Cross, Suikoden and Legend of Dragoon. I'd highly advise anyone interested in PS1 classics to purchase them from the US store. They also run faster at 60htz as opposed to the inferior PAL 50htz versions we have on the UK store.
The only possible downside I can see to getting them off the US store is if you plan on playing them on the Vita. If your Vita is locked to a UK account then it won't allow you to play games from other accounts. You'd have to restore the factory settings on the console and insert a different memory card before you could play PS1 classics on it which is a right ball-ache and a real cock up on Sony's part. They should have made the Vita like the PS3 where it can have multiple profiles on the console and anyone on that console can access all games. I hope that Sony eventually add this feature eventually otherwise I won't be able to access my entire PS1 library! Still, for anyone not too bothered about playing PS1 games on the Vita, the US store is miles ahead of the UK one.