Good idea to sell the car if you're not using it enough and now, or before the bubble bursts which might not be for a while yet.
For seat comfort have you sat in the front passenger seat for a journey of reasonable length as that should give you some idea of seat comfort for you. Seat comfort can be a personal thing, generally being short I dislike German car seating. Your Fabia seat sounds like it might have had more stress than normal, big person, mobility issues, deliveries driver.
If the scuffy won't cause rusting then why bother until you really need to. My wife's previous car had a long rear panel that somebody dented and disappeared, she put up with it for 18 months until the servicing garage gave her a good quote on the repair (they must have need work at the time). I speculated that within two weeks the repair would have a ding from the public car park at her work, not even 24hours, she was so annoyed.
If the car has only you and not a lot of heavy work stuff to carry too you should find the performance reasonable, handling won't be up to S3 but the use of speed and acceleration tends to be very restricted nowadays anyway.
If you want more mpg pump the tyres up to 35psi as that noticeably reduces rolling resistance you lose a little on the handling but that can put more fun back into actually driving the car, different perhaps to the heavily(?) assisted S3. Course smaller wheels with narrower tyres would be more practical too but that's not the fashion.