Competitive players are your only source of bowser players, no one can know how many casuals there are that play as him, but a medium you could use is the post counts in the bowser thread for Melee. Fairly small compared to some of the others, especially for the #1 demanded character for a game.
Your second point has a flaw as well. You see, I do know people who *will* play as Krystal. Check The **** Staff and you'll find a group of people that will play as her. But one thing you have right is there isn't an accurate number of people who will, without a shadow of a doubt play krystal, but thats true for any character.
Finally, SWF has a huge competitive community, and therefore don't favor Bowser too well aside from his roles outside of smash. So it really isn't that sad that Bowser has less votes, considering past events with Bowser, and the possibilies Krystal has for brawl.