Our house was in pretty good nick, all told, when we put it on the market (got out of the US market *just* in time last year!) in late summer. The big thing we did was tidy tidy tidy and clean clean clean. We had fresh flowers in pretty much every room, every day. We had kept small tins of paint when we redecorated the house, and I retouched the paint around the house, including the gutters. The flower beds were always weeded and watered, and the only thing we actually changed in the house was the taps... they were the cheapest on the market a decade previously. I think we put a total of $100 into the house!
Good luck.