Usually the interest for my goes right after getting the car restored so its mint,then I usually break it.
The fun for me is finding a car be it knocking on a door,out raking about or off eBay,finding the parts,winning auctions on eBay etc.
After it's done and I drive it that's usually when I lose interest.
Had my 16i since march I think and almost put it up for sale in October as it was almost a new car with all the bits I managed to buy,nearly everything was correct,radio,mats,brackets,suspension,tyres etc but I was bored but instead I sold my other 16i and the pile of parts I had collected just in case and spent the money modding it so it was actually the car I wanted instead of the car that ford built.
It's not finished yet as I'm still upgrading the brakes and stereo but I now go into the garage just to look at it and take in all the work I have done to it which is very rewarding.
I don't think I'll sell it now and last week I bought an escort cab I built years ago but sold,that won't be going either unless I need the money for something more important like the house or family.