Is there a relatively painless way to find out which players have never, or rarely been used without methodically clicking them on one at a time?

Salary changes are based on usage. So, those players whose salary has decreased, are rarely used. How you actually identify these players is not always that easy (particularly given that the top 50 just lists the expensive terrible pitchers). If you have an old salary spreadsheet you can compare it to the most recent one to identify these changes.

I don't know if I'm really allowed to do this but this is from what I have on my computer (most to least expensive)

pitchers
https://drive.google.com/open?id=0B2FozEGXCxjEQnItUWlBMHdvMWc

hitters
https://drive.google.com/open?id=0B2FozEGXCxjEUExlamlNMGstMTA