That's a shame, but as you say, it has a lot going for it, and by the sounds of it not a lot to put it right. Did you put a code reader on, sometimes they have hidden codes as to why its labouring, could just be a plug or a coil, but then it could be something sinister as well like a fuel pump, injectors etc.
If you keep thinking about it, get him to run the car a bit to stop it labouring as he says its been sitting, MOT it, calculate what it will cost to have the paintwork done, double it, and then knock him down.
Its going to be hard to WOW you mate, I know exactly what you mean when its Meh! Your expectations must be similar to mine which is probably to high for a 10k toy!! this is magnified by the beast and RRS you have as well. In short its called being spoilt, and its hard for any other car at this price point to measure up. Being a Petrolhead and having perfection, comes high expectations. I have walked away from cars that really someone would love and buy, because I am used to top of the range mint perfect beasties, I think and I want better!
I cant help but think whatever you get you wont have it long, and do some wheeler dealering with it and want something better, if things get sorted, you can always sell it, then you can say you have had one at least. Just get it cheap enough matey!