"one helped me out without intending to by talking about why one feature probably wouldn't work without a tweak because they found out it doesn't work without X."

Didn't you just disprove your whole point there. Your competitor revealed his/her ideas about how to solve a problem (that you hadn't even foreseen yet going by your description) and in the process hurt him/herself in the marketplace. Your advice of meeting and talking openly with your competitors didn't really work out for that person.