Agree that 16 is too many for two reasons.
1) When you get to #16, you're seeing teams with 3+ losses. "Deserving" is the key word here others brought up.
2) It seems year in and year out, you can draw a pretty clear line somewhere in the range of #6 - #10 where you see a clear separation between teams that can compete with the #1 - #4 teams if they played a hypothetical 10 game series and those that would really struggle. Granted, this year is a little murkier, but I'd draw this year's line at 8.5, just to see what UCF could do.
Someone brought up the scenario where a team starts slow with a few losses due to a key injury, youth at key positions, etc, and misses their conf championship as a result; however, they demonstrate undeniable potential to win a playoff down the stretch. Eight slots gives you enough room where a committee could get that team in, where four is too restrictive. No such scenario in the recent past comes to mind, so this doesn't concern me a great deal.
I prefer eight, but could get on board with a 12 team concept with first round byes for 1-4.