I own both. I have plenty of room to transport, size and weight isn't a problem. Floorspace is never a problem.
When I use my single kick I have to cram the toms in to fit my hats, and I can't (well, comfortably) use all of my cymbals, because there just isn't enough room to reach all around without putting them in front of me. On the downside, I can't (comfortably) squeeze in my two floor toms if I have two basses, but using my second bass allows me to space out my toms and cymbals, and makes ME feel cooler.
And I think that we'd all agree that when you feel better about the kit you're sitting behind, you play better. Sometimes I have to practice on another drummer's kit, and he has a completely different setup. I'm just not comfortable behind it, and don't like it, and I usually don't play as good.
The main reason I own both is because I like to change my setup every other week or so, keep me on my toes! If you FEEL cooler/better about using two basses, and have the freedom to do it, I say go for it... If it doesn't make that much of a difference, or you don't have the ability to transport it (c'mon guys, its ONE more bass, not THAT big) don't do it.