Close encounters with kerbs and potholes can make wheels look scruffy, but you'd be surprised what can be repaired without even taking the wheel off the car. There are mobile repairers who restore alloys, and they typically charge around 50 per wheel.
Small bodywork scuffs and scrapes can easily be fixed. It's also possible to remove dents and bumps, as long as they're not too severe.
The trouble with most repairs to wheels or bodywork is that a dealer can get the same work done for less money - sometimes as much as a quarter of the price.
If you're going to part-exchange your car, it probably isn't worth getting expensive repairs done.