This is a really good thread.
Yes
It depends on what you are selling. Small cons have cheaper tables, but lower attendance (not as many wallets on the floor so to speak). I tend to try out new products at small cons, to test the waters without too much risk. The big cons are more expensive, but high attendance means more sales. I bring a lot more stuff to the big conventions. It's a lot more work and a lot more pressure, but its also equally more fun and I make way more money.
Not being seen has more to do with convention set up than size. TCC one year put similar vendors together (all prints artists in one row, all crafters in one row, etc) and it was a disaster. PCC one year took the autograph signing off the main floor and it killed vendor sales (no one wanted to wander down to the vendor floor). This year at PCC was the biggest year yet, added 1000+ more vendors than last year, had a gunman try to kill people, and I still had fantastic sales even with all that.
This is a problem with any con. Indie comics are just not as popular as fanart. Everyone struggles with this and deals with it in different ways.
I both agree and disagree. At really small cons I get to spend more time connecting with potential fans and getting to know them. Its easier to make a good sell to them. However, I sell substantially less at small cons. I easily sell 5x more at a big con like PCC. I might sell a lot of comic books there, but not talk to a single person who is buying the book (too many people at my table making purchases to really talk to any one person). So it depends on what is important to you.