Another factor in the enjoyment quotient (EQ) is the quality of the time for the repair.
If there is a high expectation that the repair be finished ASAP, that added stress diminishes the EQ.
I find the projects with the highest EQ to be those which have no definite, or at least no immediate deadlines.
Rescuing my '64 Falcon Sprint Convertible from the crusher was one such project. It took years of available, free time. There was no rush, or demand to be "done". I was able to work when I chose to, and walk away when I wanted to do that.
I just finished (almost) a small addition to my house. Very high EQ overall--except when I get pressure from she-who-must-be-obeyed for some finishing detail that cannot be done at this point. This makes for stress for both of us.
This probably explain why I do not make my living doing car repairs. I can do it; I have the tools, skill and knowledge. I could probably even make more money doing car repairs than what I do to support myself. However, the pressure of constant deadlines of people waiting for their cars would probably make for a miserable work day.

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1982 300SD " Wotan" ..On the road as of Jan 8, 2007 with Historic Tags