If you are too worried about the value of your car you might as well not bother modding anything. Mods never really add value to a car and they reduce the resale market who would by the car as certain buyer groups wont buy modded cars and you are relying on a future buyer to have the same tastes as you.
Also to answer your question "would anyone want a modded alfa with 120,000 on the clock or more??" with another question, how much is a non modded alfa with 120,000 on the clock worth? Even the rarer models arent worth much with that many miles on the clock.