It's not worth their while to replace defective boards that are outside of the warranty period. You might wanna buy a service warranty similar to what guitar center or amazon offers. I know guitar center swaps that shit out without any questions.
Shit breaks though man. It's a computer. Computers die.
I'm not even gonna get into the whole "I take care of my equipment" argument because I'm sure you do. Sounds like you've had a run of bad luck. Make a decision. Is the equipment worth it to you? There are other options out there. Maybe give them a shot.
I beat the living hell out of my cdj's and I've only had one give me an issue (cdj 2000). I got lucky and reseating a few cables fixed it. It still acts up once in a while though but I get it, it's been through a lot.
I've had cdj 800's, 2000's, and now the 2000nsx2. Sometimes it's just the luck of the draw.
Try not to sweat it though man, it's only money. Hah. I feel ya though, life can be a bitch.