I have pretty much always used primer. I've used balsa sealer a few times and for your afore mentioned reasons, I've all but abandoned the practice. I get great results with just using primer. I use primarily gray for starters usually 2 coats (then sand) and then another coat (more sanding). I'll shoot a last coat of white (with a final sand) if the rocket is not going to be white in it's final color. I do sand the balsa sheets several times using different grits before removing/cutting the fins, which kinda helps to lessen the grain somewhat.
I occasionally fill spirals with Fill and Finish (or whatever it's called today) but the sprials have to be "big". FNF generates way too much dust for my likes.

Occasionally there's a grain or two that peeks through, but I'm good with that. After a flight or two there's usually going to be couple of dings anyway. OTH, with your showroom finishes that may not be acceptable to you.

I guess everyone is different and it boils down to how much time you want to spend sealing, priming, and sanding. It is supposed to be a hobby.

__________________
Dave
Fire is the leading cause of fire.
Was once SAM#0132