Not quite.....auto techs work against a flat rate. If they can beat the flat rate, their hourly wage increase, if they take more time than quoted they loose money, right on time they break even. Most good auto guys at a profitable dealership make $30'ish per hour....again they're always chasing a flat rate.
Plumbers is a non-union vs union thing.....if he's union, he's making journeyman or master pay set by his local. If he's non union, he is bidding by the job.....prob a more similar situation to what a full time luthier is doing, bidding a job. The more time he spends, the less money he makes...the the less time, the more money cause now he can get to job #2 that much quicker.
I am an Aircraft Mechanic by trade...and I agree with what has been said previously....skilled craftsmen (in any trade) are things of the past and vastly under paid for what we do. In my profession, guys can make as little starting out at $10 p/h all the way up to $50 p/h. UPS, FEDEX, and SWA are the three top paying gigs in the Aviation Maintenance world. I top out around $45p/h....and yes, we are union....for better or worse.
As far as luthier is concerned, I think pay would have to be somewhat contingent on your lifestyle and location. Does your lifestyle and geographical location allow you to live comfortably on $50-$60K a year? Do you need more? I dunno? For me, I couldn't put a price per hour on doing something I love (I am not a builder but would love to be someday). I can put a price per hour on working for XYZ company while doing something I need to do to get by and feed my family. So I think as a luthier you need to look it at like, how much do I need to make per year? Then, how many basses will take per year to reach that goal? I would much rather put in 60-80 hours per week working for myself doing something I love than working for the man at 40 hours doing something I would rather not be doing...even if at the end of the year it equated to the same amount of money.
The only caveat is benefits....working for the man, its part of your compensation package....working for yourself, they are not.