Thin coats would be great if the cans didn't say "do not thin" most of the time. We too buy foam brushes in bulk (can't figure out why you pay single brush list price for the brushes from Jamestown when you buy a 48-brush rack ?).
Maybe I'll ignore the instructions and do aggressive thinning to see what happens.
The Captain's Varnish that I like says something like "thinning is not usually necessary" but I usually apply two or three thinned coats and a final coat unthinned. A guy in my previous marina (who looked like the inspiration for "The Old Man and the Sea") recommended mixing Flood Penetrol and varnish 50/50.