Meanwhile, back at the OP...
It's really not impossible to dive balanced and wet in the tropics, unless you're carrying an insane amount of tanks. I'm barely buoyant at the surface in a 3/2 wetsuit, but I can swim twinned AL80s and two AL80 deco slings up, even wearing a steel back plate. If your buoyancy failure occurs at the start of the dive and your twins are full, you have little or no deco obligation, so consider one of those slings ditchable weight if you have to. I'll drop a tank before I'll drown... If it's later in the dive, your twins aren't going to be that negative, cos you'll have used gas. If you're using stages, you breathe them first anyway, so if anything they become a buoyancy source as long as you're using AL80s. Often, too, if you use AL80s for deco gas, they won't be much more than half full at the start of the dive unless you're doing something really big, so again, not that negative. Notice how many times 'AL80' crops up in that? Balanced always has to be the starting point, because even if you want to use one of the other solutions, it's easier if your rig is balanced.
For a little added comfort and ease, I do carry a couple of liftbags, and I do practice ascents using a liftbag as a hand-held buoyancy device every now and then. Had to do it for real once, too, having had my wing let go at 180 feet. It's not really a biggie, although your arms get a bit tired towards the end of a longish deco ascent. In a pinch, an SMB will work - you just have to hold the top and the bottom in one hand so that the dump valve is at the top of the loop you've created. Done that, too, although only in practice. Less tiring than climbing a line under a surfaced bag, that's for sure.
If I'm diving sidemount, I like to use Catalina C95 alloys. Horrible tanks under any other circumstances, but they trim out beautifully SM and don't go 'butt light' until they're down to less than 1/4 full, which I'm mostly aiming not to get to. Heavy, though, so I do use an SMS100D dual-bladder rig, although in part that's just because someone sold it to me cheap... I've grown quite fond of it, though. The second inflator is not hooked up - it's perfectly easy to orally inflate if you need it. On the other hand, the wife uses a Dive Rite XT and I've seen her comfortably inflate and use an SMB in a practice failed-buoyancy ascent while sidemounting heavy C95s.
Not that I've got any objection to tropical wetsuits, though. I'd love to get one, mostly to get away from salt-water chafing when hanging about in a wetsuit all day as well as for redundant buoyancy, but it's regularly pointed out to me that there are plenty of other things I could usefully spend the money on and nappy-rash ointment is cheap!
Hmm. Looks like I either do or happily would use all of the apparently exclusive possible solutions to a buoyancy failure, in varying combinations. Does that make me evil?
I'd post a profile since it seems to be the fashion, but all I did today was 25 minutes at 48m to see how the shark population is doing along a stretch that got pretty badly fished a few years back. It wasn't a very interesting dive, unless your idea of fun is being chased along the base of a wall by a bunch of over-curious Grey Whalers. Which, actually, is my idea of fun. Oh, and look, I got to post a profile, too.
