Oh Im well ahead of it on providing additional cooling. Before I even started professionally repairing electronics, I was over-clocking PPC modules for Macintosh computers. Over-clocking required updated cooling, and with the help of another individual, I achieved a 733MHz -> 933 MHz over-clock on a 7450 PPC CPU (approximately 1 generation behind the PPC used in Xbox 360s). And also, indeed, the stock x-clamps are pretty lame. There doesnt seem to be a consensus on a single way to do the X-clamp mod; so I devised my own way, which unfortunately still needs tweaking, though my way could work as-is.
Anyway, I really bought this 360 to repair and then use. Im not trying to make a business out of 360s, though I wouldnt mind repairing a couple other than the one I have.
$25 each aint too bad for you. I am professionally repairing electronics which cost on average about $1000, and Im only getting paid about $15 to $20 per unit.