You can go with stock CTR cams (more aggresive than the ITR cams)

A few of my friends run the Stage 1 cams from Skunk2 and you do get some good increase out of it.

Valve springs are suggested cause the stock springs aren't stiff enough for the new cams. If you had the extra money and the time i'd go ahead and replace 'em with stiffer units. Not everyone does, but it's def. a good idea.

Yes with adjustable cam gears and some tuning you'll get good gains. You'll spend some $$$ but you'll get noticable return from it.