I paid a professional to detail the black XJ8 I had once, it looked fantastic afterwards and I would do it again in a heartbeat when I have another car that I love. I spent a lot of time on my 540i myself, I spent more than one weekend trying to detail it myself but at the end of the day I don't have the proper tools so I could never get the finish I wanted ...and I had a wing without lacquer on it (don't ask) ...so that was never going to be right either. Still I was happy to spend the time trying because it was a car I loved.
However the Volvo I have now, no chance, I pay some Iraqi's a fiver to clean it every so often, I have never done more than vacuum the inside and apply glass polish myself ...nor will I in all likelihood. It's not a car I really care about, certainly I was annoyed when some prat put a small dent and scratch in the door in a car park, probably with a trolley or something ...but I didn't howl in anguish and swear to avenge my car like I might have done with my black Jag ...again because it's a diesel Volvo estate ...I will always keep it in good shape, but I'm not going to lavish love that I do not hold for it, on it.
Point is, it really depends on how you feel about your car I suppose. I use myself as an example because I can well understand both sides of the argument, as to me, it really depends on the car. If it isn't one I care about that much, then I wouldn't bother with detailing, if it is, sure I would.
I would like to stress that I take very good care of all my belongings though, but I only really get 'obsessive' about the ones I love.