Yeah you tend to find that certain pc parts hold their value very well on ebay and the E-8xxx's are one of them. Obviously if you had a high-end mobo to go with it it's even better.
But yeah in your situation it's probably best to upgrade a part at a time. Also - your memory is probably worth more than DDR3 is now, I know that's crazy but DDR2 memory is more expensive than DDR3 in many cases. I noticed you said it was 1066, is it Corsair Dominator? If so that's gonna net you a good amount back as well, in fact chances are any 1066 DDR2 will get you some cash back which you can use to get cheaper DDR3 with.