Dividing gamers in half may be unattractive, but there's only so much you can do to compensate for non-mouse controls. Giving the player an aimbot is potentially very evil. Were the PSP a touch screen like the DS or infrared like the Wii, you could maybe do something with that, but basic D-pads and joysticks are terrible against a keyboard+mouse.
Also, giving the player auto-aiming may still not help. Much of Quake DM is shooting where the target will be, not where he is. With a rocket launcher you fire at the ground where the enemy will likely be in .5 seconds or so. Nails travel quickly but they still require some leading. Adding these things as aim helpers to the engine would be a very bad idea -- it takes all the Quake out of Quake, and turns the player into a pilot (I just steer and press the fire button) instead of a combatant. Doing any less than that, however, may turn out to be too little to level the playing field.
Trying to get PSP and PC controls to compete fairly with each other is a big problem, bigger than I think we want to deal with. Even though different network codes divides the community in half, it's better than combining players under unfair terms.
Think of it this way -- if you're a PSP player, do you really want to end up on servers with PC players? Or do you want PC players to be able to join your games? Almost no matter how good you are, you're going to get stomped.
If you're a PC player you might care less because you get to dominate, but would you want a PSP player on your team? And is it really that much fun to trample players who take half a second or a second just to turn around and aim at you? Frankly, that's not my idea of good sport.
Whether I'm on PC or PSP, I don't want to mix the two unless both sides have agreed in advance.
Aim enhancements will only take us so far, and (if too ambitious/accomodating) may demolish what makes Quake DM what it is. They won't level the playing field at all, unfortunately. That's my opinion.
And besides, there's one crucial thing to understand here. We're not dividing the community in half. We're not taking a huge butcher's knife and cleaving off a huge chunk of the existing community. The PSP community is just getting started, and personally I'm fine with them being allowed to develop on a separate netcode protocol.
After all, QW would not be as strong as it is if it had not been allowed to define its own protocol to improve network latency. The PSP's need is different (not net efficiency but controls fairness), but the need may be just as great or greater. IMO the PSP community may not develop nearly as fast if they can't play multiplayer without some PC player coming along with a ridiculous controls advantage and stomping them. Giving them their own fair & safe PSP-only servers may be the best way to encourage people to play PSP Quake online. Otherwise why bother?
At the very least make it a server option in the menus:
Platforms Allowed: {PSP only (default)} {PC only} {Any}
Just my opinion, not necessarily fact. I'm sure people will disagree and for good reason, but at least consider what I've said. Engine aim helpers may help, but I don't see them going far enough without going too far.
(lord I'm chatty today. Sorry for the wall of text.)