paul - to be fair, i think michael has a good point. as far as modding a car - too many different people have differing ideals when it comes to modding. in respect of mods - i think the market of late has shown us that it is a very personal thing with people, hence the difficulty with making back money spent on mods. most of us are aware that by going down the modded route, there is a very good chance that you will not be in a position to re-coup your costs - this is merely a function of the market place.
as to the desirability of your car, i'm sure that a relatively (?) low-mileage Uk 6spd will fetch better money but the question is whether in real world terms, will it fetch significantly better money (like what you think it's worth)? so many things are co-dependent on achieving this price ie potential buyers wanting to have done exactly the same mods, the market-place on the day etc etc
i just feel that if you are happy with the car and feel it is worth 16k to you, then so be it (especially since you aren't selling it). with respect to everyone else's opinions, potential buyers may not feel it worth that much and you have to respect that as well. i hope that when you do sell it, that it fetches what you think it is worth but i am just saying that you should be prepared for people not to share your views on it's inherent worth. in the end, needs must .....
as for the performance issue, i don't think i am in a position to comment ........... all of the above is just my 2p