I'll half agree with you, that who the show's lowest common denominator is does have to be considered. I'm also admittedly guilty of mental masturbation from time to time, in that I spend too much time thinking about stuff that probably doesn't deserve that much effort. But who said masturbation was a bad thing?
And compared to other shows, I'd say Lost is on the intellectual side of things. At least parts of the show have been. Walt comes to mind... what are his powers, exactly? Did he manifest that polar bear himself? Hints like that keep us guessing. And that's why the jury is still out on Lost. The show has had its viewers come up with some pretty wacky theories as to what's going on (theories like that they are in purgatory), but it's yet to really deliver anything tangible. And if they never do, they'll lose viewers like me who *have* spent some time thinking about the show. So I guess it just remains to be seen... how ever they answer the unanswered will show who the show is really for, I guess.
Hmph, an effective way to get people to watch, no?