You are right about raising more preflop....limpers tend to call a 4xbb raise all day. As for the flop...do you bet out trip nines this hard? I have seen the occasional player do it if he has been drawn against a couple of times in a row and therefore overbets to take the pot down now. With seeing so many flops, this guy could have just about anything. Most likely holdings 2X, flush draw or PP (with a small possibility of a nine)....but for the most part I think you are way ahead (I think he has a flush draw....hence the all in). I would call here (I would have been more worried about the BB yet to act behind you).