i'd have to say yes, it worth it to mod, customize/personalize your car. if you take how much you have learned from doing little projects like painted parts of your dash, installing a cold air intake or making a custom sub box all those things add up and you know more from doing all those projects. not to mention the community and friends you met from modifying.
i'm 20, and have been modifying for about 3 years and have enjoyed learning to do all sorts of stuff, and if you can further you talents you help other modify their vehicles and maybe make a living from modifying. how many shops are out there and the owners started off by doing it to their own cars and then offering it other people. I can think of two on this site that have made a living off of thier passion of modifying cars, Tom and Hypnotic.
it's something that is definatly worth it.