Just bought an "excellent condition" 13" Unibody MBP 4GB 160GB 2.26GHz (A1278). Came with the original box and all original accessories. Was this a good deal? Mac2sell says it's worth $640, which shocked me. 
I have the same model, mine is in MINT condition is 29 months since build. I have added 8gig ram from OWC as well as a OWC 120gig SSD I wouldn't take that price for mine with the mods but I think your just fine with where you are on cost. It's a great machine and should give you many years of service. If you make a few mods like I have it will be the hottest little pup you could ask for. Super well built machine runs cool and can run away with anything that I have ever thrown at it... I paid $1050 for mine before mods 24 months ago I still think it was a great deal... ENJOY.....![]()
I think you paid a fair price
It's a decent machine too, the newer ones are faster, but that doesn't make yours slow by any means. I've got a 2.4 c2d 15" macbook pro and it isn't "very slow" and doesn't "lag tremendously running flash" like robbie12345 says.
Just enjoy it.