I've enjoyed the 48/3rd place - so many countries had something to play for in the final group game. We had 3rd place teams go through in 86, 90 and 94. When it went back to 2 through from 98, the group stages lost a bit of something for me.
64 is nonsense imo - just too big and it'll be a bit like the Olympic with some appalling mismatches.
The world cup is meant to be the best of the world, not crap teams making up the numbers.