Believe it or not, I'd actually pay 60 bucks for Spore... easily. Plus 10 bucks for the full Creator. Every game's a gamble, but if Spore is even half of what I expect it to be (and my expectation have been reduced over the last three years), it'll easily dominate my PC and my time. We can do a price comparison:
World of Warcraft costs 15 dollars a month (US). Thus, the cost of WoW for six months is 90 dollars.
Spore could cost a total of 70 dollars (with the editor pre-release). Assuming you play Spore as much as you play WoW for 6 months, you come out ahead.
Now expansions are a different story and I'd guess expansions, like those of the Sims series, will produce the bulk of the money. 30 bucks for an expansion upon release isn't too heft, IF you make heavy use of it for at least two months.
No matter how you cut it, if Spore does take off and produces as much as it boasts, it'll easily be a value. The real question comes in this pay-per-part crap. To be honest, I'd rather have them just release a part a week/two weeks or something for free and save the majority for new expansion packs. Nonetheless, DLC and such is catching on and though I hate it, it's here to stay.