Two really good arguments here, but it seems to boil down to two camps (for me anyway)
I like to build
I like to drive
Don't get me wrong, I love my Z and driving it, but what I cherrish most is that I dismantled and re-configured this car to be what I wanted it to be, and it started up and drove when I asked it to. It's hard to describe what I felt when I drove it around the block the very first time, but after that it hasn't been the same. I guess for me, it's really about making something and getting it to work, and I guess I wouldn't have learned that without going through this process. That's pretty hard to put a price on, when you think about it.
I find myself looking for another project to build, always SOMETHING to build. Projects don't necessarily need to be a cars for me either, right now I'm doing some remodeling at my mothers house, its new and challenging work, eats up my time, but only her bank account