I don't use flash that much, but when I don want to view some funny flash animation or some other novelty, I'd have to start up a 32 bit firefox..
firefox32 (in my case)
It's easy enough to set up and I don't think it's all that bad (I have some 200 megs of 32 bit stuff on there, not just browser with flash, also some wmv codecs etc)..
As long as the libs are set up correctly (and there are tons of tutorials on that) you can run 64 and 32 simultaniusly..
For stuff like Wine (or Cedega) it's a bit harder but still doable..

But yeah if you want all everything to work out of the box you should stick to 32 bit..
And be sure to mail to Macromedia for a good 64bit linux version !!