I've got a Miller 175 that has it's share of annoyances. Mostly the stock gun and ground clamp were garbage, but the gas solenoid sticks occasionally (once a year or so) and it's duty cycle is about on par for a low end 220v machine, meaning low.
I also have a Miller Dialarc 250 HF tig that hasn't had a hiccup while being 25 years old and has more power, even on an under rated 60a breaker, than I could ever need for vehicle fabrication. I haven't had to use it as a SMAW power source yet but having 3 ranges to dial in for DCEN and AC with the tig torch have been invaluable. Nothing short of DRO's would suffice.
I would replace the 175 with a 210/212 or 251/252 in a heartbeat if I found the right deal. It's not worth going from used to new money wise, but used to used would make sense.