I've been offered that position a few time in the past 10 years and they couldn't sweeten the deal enough for the extra hours and responsibility. You have been in this deal long enough to know how the service manager gets the crap storm when the hours are down. I think I offended the GM last time when I told him I couldn't afford the pay cut from my flat rate master tech wages. So now I'm sitting at home collecting unemployment checks and healing my abused body from 40 years of being a tech.
I would do that job if I didn't have to deal with the thirty-somethings who have zero long range vision. We have a very young management staff that know nothing about the car business other than when to kiss the owners daughters butt.
I wouldn't do it because like Guitar said they will engineer ways to weasel out of paying your bonus check every quarter

Gus