: Is 1200 grit wet sandpaper too fine a grit for sanding between coats of
: varnish?

I build some furniture and coming from that side of the equation, yes. I use that for polishing the finish, not for sanding. I would use a something like a 220 grit maybe even 320. Just which ever I had laying around. Your just looking to scuff up the surface, not remove a lot of material so you just lightly sanding.