Should only be able to increase a given maneuver twice (for a +4 for 1 point). I'll make that clear in the text. So at that point you have your +4 to trip, and have another 6.5 points to spend elsewhere (for higher crit, damage, bonuses to other maneuvers, extra damage types, etc). And you'd still have to pay the feat for the exotic weapon proficiency. And of course as you note, new weapons are something the DM should adjucate carefully, to prevent any serious abuses I haven't foreseen.
Ah. That makes far more sense, and there aren't really any other easily-observed abuses. Only other thing is that I don't really think 'able to do nonlethal damage' warrants a full +1- maybe a +.5; it's not exactly as strong as a Reach weapon, after all.