I'm in the middle of putting my ceiling panels back up right now. I had a similar back-and-forth conversation with myself, trying to weigh the pros and cons. One thing I don't see mentioned much is the flammability of the wood ceilings or the nasty smoke that FRP or other plastics would put out in case of fire. Between the fireproof-ness, the free-ness, the school bus asthetic-ness, and the thin-ness (I'm also a tall guy), reinstalling the ceiling panels seemed like the best option for me.
BTW, my ceiling panels are aluminum, so the pros and cons are a bit different than for most folks with steel. No magnetism :nonono: but they ARE nice and light.
I'm planning on updating my build thread with "lessons learned" as soon as I'm done putting the panels back up, but here are some thoughts for the time being:
If you spent the effort to remove the ceiling and re-insulate, then don't put the panels back directly on the ribs. Get a thermal break in there. Even if it doesn't work, at least you will have tried

. I'm not speaking from experience here - this is my first time doing most of this stuff. I'm just sharing my opinion that doing all that work and then having massive condensation issues would be heartbreaking.
My attempt at a thermal break is lengthwise strips of 3/8 plywood, with cut up pieces of blue foam camping mat in between to cover the exposed ribs. The blue foam mat was an afterthought, and I'm not sure it'll help much. The plywood is attached to the ribs with countersunk #12-24 Type F thread cutting screws, which perfectly thread into the holes left behind by 3/16" rivets (
https://www.amazon.com/dp/B00GYJBS7U/ref=cm_sw_r_cp_apa_fabc_pm84FbPW0PND8?_encoding=UTF8&psc=1). I've shifted the ceiling panels forward 1 1/4" so that when I screw them to the plywood slats, the screws don't touch the steel ribs.

Sorry for the rotated pics. I'm doing this from my phone.
To get the panels back up, I temporarily put up more plywood strips about 1/4" to 1/2" below where the bottom of the ceiling panel will rest on either side of the bus (several inches above the windows in my case). You can kinda see these strips in the above image. Once you muscle the panels up onto those strips, the curvature holds them in place until you can screw them.
If you do put them back up, a second person is very helpful. If you're on your own, one of those "little giant" style extendable ladders can be helpful to hold one side of the panel.