First off, I am in agreement with all who hate the idea of expanding to 96 (which is to say, everyone). It obviously waters down the tournament and is completely unnecessary as it relates to accomplishing the real goal of the tourney: crowning a worthy and deserving national champion. Heck, the 65 team field is already too large (seeing as an 8 seed is the highest seed to win, 32 teams would work), but since they give automatic bids to all 31 conferences-including those that have no chance of producing a NC year to year-they had to go to 65 to provide a balanced tournament capable of including all championship caliber teams.
I will say that I really haven't heard too many people arguing that it better accomplishes that goal than the 65 team field. Most of the NCAA brass have said that they view it as giving a "reward" to more teams for good seasons (bullshit if you ask me I'm sick of the "everyone gets a trophy" mentality permeating our culture today), and some have been even more transparent and let the real reason (more $$$) be known.
Unfortunately they are probably right. Pools are important to ratings but getting 32 more games on the air will off-set the slightly lower ratings and ultimately gain more money for the ever greedy NCAA.
As for the secondary topic of whether or not a football playoff would better decide a national champion than the BCS, I think that answer is a resounding yes.
For those that think a playoff would water down the regular season, I ask what exactly does the regular season accomplish now? IMO, it really only determines which team is the best in each respective conference (Note: except for our beloved B10, which neither plays a round-robin nor has a conference championship game). The sample size of non-conference games is so small (and the matchups between top teams from each conference smaller) that we really base relative strength of conference on nearly complete conjecture (and seem to always forget when doing so that the transitive property does not apply to sports). Then we usually use these relative strengths of conferences to determine who the best of the Conference champions are, and then somehow select the "best 2" to play in the BCSNCG. I think that sounds ridiculous and not in the nature of competition, and thus makes it obvious that a playoff of some sort is needed.
Now the point brought up about "well how big and where would it end" is legitimate, and IMO major conference re-alignment would be necessary so that all conferences have a championship game or round robin format and some smaller conferences get combined/eliminated. But without drawing up a huge plan and hi-jacking this thread further, I think nothing greater than a 16 team playoff would be necessary and I think it would always crown a worthy and deserving champion.