My general thought process is;
If you played Civ4 from the 'get go' - you'll probably enjoy this more(seeing as Civ4 was a mess sans expansion).
If you played Civ 4 only after the expansions you'll probably like it less, since it's got a lot less 'polish' in both bugs and gameplay mechanics.
If you've never played a Civ game, Civ5 is probably the 'easiest' to get into as it's developed with the idea of brining in new people.
If you've got a barely-minimum or even barely recommended PC you'll probably not really enjoy the game; at least not mid->late game.
I couldn't imagine spending 60USD on a game...lol. I don't think I've paid 'full retail' for almost 10 years now. You should really look into pre-purchase and sale deals
That being said, I think 1UPT is what makes the game a lot better. Stacks o' Doom in Civ4 were some of the most boring and irritating gameplay 'mechanics' I've seen in a strategy game - ever.