Teachers are not paid peanuts, nor are they monkeys. The teachers I know aren't particularly wanting to be paid more, they'd just like less paperwork and for the government not to move the goalposts or bring out a new initiative every 5 min.
Very much depends on how headteachers view the subject. If the head values the subject eg Maths, you’re sorted as a Maths head of department. Looking at all the hundreds of adverts I’ve seen recently, it varies massively. My headteacher removed a room, a teacher, a lesson a week, my office, my second in charge because he didn’t value my subject. Nothing personal. I left for a job with fewer students, less money.
As an Head of department, the added responsibility (TLR-teaching and learning responsibility) varies from about £2000 to up to £13000 (rare) same size schools, similar job description. A ‘good’ head of department payment, IMO, is TLR 1B, over £9000. In my current school, the TLR is 2B, about £4442. Money is definitely a consideration.
You’re right about the new initiatives, tho. If I have to attend any more of the utter bollocks trainings which aren’t improving my teaching or helping the children learn, I’m going to get very pissed off. I’d rather be planning/marking.