when we were messing about in the office on webuyanycar.com (yes, annoying isn't it!), they offered £8155 for my UK 54 plate (which has done 44k). Not that I'm selling, it's just interesting to see what they'd pay for it compared to the market list price....
I guess you could get a bit more than that though given the parts it's got on it even if the interior's a bit nackered. Either way you go, I guess you'd end up spending about the same, but if it were me, I'd get way more satisfaction from doing it up rather than replacing