We paid 7500 Euro in 2006 for an '05 and we got 4200 Euro for it when we traded it in June of last year. Our current car was a BMW corporate car so it was about 9 months old and had never been titled nor was it particularly expensive.
Do you know if the dealer paid you less for your trade-in a result of the rental status? Not bad at all since you've owned the car for eight years.