Not a dumb question at all. I left my Tufte books at the office, so I can't check, but I thought he cited sources throughout.

Either way, between Cleveland, Robins, Few, and Ware there're tons of studies and references:

Better is subjective though and related to what you're trying to do. A lot of past research was about efficiency of information transfer. There's more recent research looking at memorability. In one report, different graphics could have both goals.

There's a "Useful Junk" paper delving into that topic. There's a link to it in Few's reply: http://www.perceptualedge.com/articles/visual_business_intel...

There's plenty more. Stanford Vis group is a fun place to check from time to time: http://vis.stanford.edu/ Heer specifically has a range of papers and some online slides for a vis course he taught http://homes.cs.washington.edu/~jheer/ (uses Tufte for the course text)

I'm drawing a blank on a few others I find informative...

Unfortunately, I don't have any about fonts but I'm sure there are plenty out there.