I think the Spurs for the last two seasons (08-09 and 09-10) have really gotten away from running the offense through Duncan in the post. I don't think he has fallen off that much to not be able to post up Frye. The Spurs offense is very guard happy in terms of running it. I know it is a product of a lot of things like the guards being good, Duncan declining with age, and defenses but it just seems like they are not taking advantage of him sometimes.
Spurs need a legit C to be finals contenders. With their current cast, getting to the playoffs might not be an extremely big deal, but they won't be finals contenders until they can get a little younger, and a good C. Bonner just can't cut it. But then again, most teams need a good C, or at least 2 average C's to contend well. OKC, Yao-less Rockets, Orlando, etc. You could even argue that Shaq and Big Z are necessary in Cleveland. Hill / Parker Ginobili Jefferson Duncan C (someone like Bogut or Lopez who can get you a double double) Would be a great starting 5.
Steep decline? Jesus dude, where have you been? Steve Francis and Tracy McGrady, now THOSE are steep declines~ Knee-jerk much?