What does too much cam lift do to a Small block chevy?

Mechanically, if the cam lift is too much for the valve springs, the springs will be 'smashed' down every cycle & you'll snap a valve spring ( or ten ) REAL QUICK. Air flow wise, if the heads can't move enough air compared to the flow that the valves can move, you'll just not use the extra lift & it's wasted. I would think that if there were to be a collapsed valve spring, you'd know it by now. Do you have roller rockers ?? If not, maybe pop off a valve cover & remove a rocker & look at the wear pattern on both ends & make sure the wear isn't going off the end of the rocker. Also, if you're still worried, you could go to a 'smaller' leverage rocker arm.