Is anything you do as a hobby a waste of time?. If its something you enjoy then why not do it. People work on their gardens to make them look nice. People work on their cars to make them look nice(in their eyes)
I've done a fair bit of tuning over the years, data logging spending fuel, but i enjoyed doing it. Getting better MPG and response for when I want the power. I've probably spend about ?2k a year on fuel for 12 years, and spent in total about ?25k on the car (including buying it) but that's a lot of fun over 12 years. People can blow that sort of money on a wedding and holiday. (gotta be careful what I say here... getting into dodgy grounds) I'd rather have the car than a wedding.... doh! I said it.
So I guess tuning and buying stuff for the car does cost money over the years, but at least you have something to show for it, rather than the lads that sit in pubs drinking their wages away, mind you they are probably happy doing that. So i guess it comes down to what ever makes you happy.
Your views mirror mine. I have also spent much time and money modifying - it gave me a great deal of pleasure at the time and I thoroughly enjoyed the experience on the road after. Its what brings you happiness, and at the time modifying did.
My guess is that Mary Whitehouse now writes on the pistonheads web site!