Depends what you mean by 'value'. To some, value is complete bone stock, numbers matching, all original, and nothing else will do. To others, value is measured by the happiness they get from their car, and what they do to it. Others still go by what Barrett-Jackson say. What are you starting with, and where do you want to end up? If you have a super-rare car, and want sonething to provide for your retirement, then making non-factory changes will deteriorate it's value. On the other hand, if it's one of 5,000 built, nothing special, then you may actually be able to increase it's value to someone who appreciates the changes. It all boils down to, value to who? You, or the guy you sell it to? My car is pieced together, I've dumped more into it then I will ever get out of it, and I'm OK with that, 'cause it's gonna be my coffin one day