Well, Ben, you already know what I think, so I'll just add this--I believe that the whole school of modeling philosophy which uses gloss coats comes from an old dictum within the modeling world that you HAD to use gloss coats under decals when the decals were really of rather crappy quality--thick and hard to snuggle down. Using a gloss coat was really the only way to not get air bubbles and lousy decal jobs.However, decals these days can be snuggled down nicely with the many decal setting solutions. I usually don't gloss anything at all under my decals.
Secondarily, there is the old assertion from Shep Paine that you used gloss coats for washes, in order to have the color roll off the panels of the model and settle into the creases. Again, if that style of modeling is your preferred one, that works great for that, but with the new trend toward filtering and tinting the basic paint coats, a flat finish actually works better for the types of finishes that I get and prefer. The flat finish has more "tooth" to grab the wash and with careful manipulation, you can really get it to go where you want.
The idea of using sealers in general is also one that I dismiss. Of course, this is because I use acrylics--and mostly Tamiya ONLY in 98% of cases--on my models. Acrylics USED TO BE awful to work with, with adhesion and fragility problems, requiring a sealant coat. But Tamiya's are nearly indestructible, in my experience. Unless you prefer solvent-based paint like Testor's enamels (such as wbill76 does) or Humbrol, you don't need to "protect" or seal acrylic finishes, in my opinion.