€7250 to go from a 2006 Civic to a 2011 Civic?
It sounds like a tremendous deal to be honest.
However the Civic they have should last indefinitely (10 to 20 years) if serviced, so if they're sole aim is to avoid depreciation they'd be better off keeping it.
It does seem a very good deal though.
That said, I really wouldnt be spending €7500 just for the sake of having a newer car. Even factoring in NCT, newer tax brackets, increased servicing etc there would want to be some pretty major fault with their existing Civic to justify spending that kind of money on upgrading. If they are happy with the car they have then Id say keep it well serviced and stick with it; it wont give them much trouble if its looked after.