Buying basses by size is like buying clothes at Wal Mart, except Wal Mart is more consistently huge. (Seriously folks, at 5'11 and ~225, I should NOT wear a medium size T-shirt.
I play a 7/8 as my main bass, but the size has nothing to do with it. There are zillions of better basses that are smaller and weigh half as much as my beast and if I could afford one I'd buy it. For me it just ends up being a trade-off, and my back comes out on the bad end of the deal both from reaching around big shoulders and deep ribs, and from lugging the pig around town. Plus I'm convinced that big, heavy basses get damaged more often and have more issues; I think gravity and inertia are hard on them.
If I were a luthier making new basses, I think I'd pick a good, pretty standard model, and start building smaller and smaller versions, tweaking all the way to see just how small and light a bass I could get before sound was actually compromised to where it couldn't be adjusted for, and then start working back the other way with that small bass to make it as good as possible. Then maybe consider enlarging it again in order to actually gain something.
My opinion is that aside from cool factor or ego, there's just no realistic call for making big basses these days, much as we love the big old monsters. A lot of times I even speak out against cutting impractical old basses just because, when a new bass can almost always do the job and leave the old guy in peace. Two sides to that coin, I know, and not for discussing in this thread.
