Jay, I haven't actually raised seedlings of any broms either, but they have "raised" themselves in my garden. Here's what I know:
Bromeliads really don't collect a whole lot of moisture or nutrients through their roots so misting with water, keeping the humidity high and as they get a bit bigger, an addition of a tiny amount of soluble fert to the misting water might be in order. I'd start with about a 1/10 strength of fert. Also when they're small, if you can manage to use rain water they'll probably do better, too. My broms in the garden tolerate being watered with my high pH well water, but always do much better - really jump ahead - once it starts to rain in the summer. I walk through the garden once in a while with a sprayer and weak orchid fert, so any seedlings get a little bit of that along with my other broms but mainly they survive on what drops from above.
They grow on tree branches (and wood mounts), on bare ground, on leaf litter and just about anywhere else they might land here, so really, they don't need a lot of soil, just something to hold on to. When I want to transplant my broms, it's usually just a case of lifting them up off the ground, then setting them down again, and staking them in place until they grab hold again. If you try thinning your seedlings, I'd bet there's not a whole lot of root system at all. A pair of chop sticks works well for moving little seedlings like that, btw. A little more gentle than metal tweezers.
Looks like I could have lots of seedlings this summer, too.
