Can I ask how many hours each aircraft flies at your school? At ours we had as few planes as we could and a maintenance company that loved to charge and nowhere else to go. I agree, I would love to remove useless instruments or replace them but it needs to be sensibly economical.
As for the temporary instructors thing, the problem stems from the fact that as a PPL(A) instructor unless you're flying significantly more than you're supposed to it's actually very difficult to make a living out of it because of the margins we work under. Career PPL flying instructors are rare, rarer than rocking horse dung. The only guys who are available are those with real jobs
but aren't as available as you would like them to be, which brings us back to another complaint which is that people don't like it when you have lack of available instructors.
It is also exploited by flying school owners who have an abundance of willing hour builders.
Club schools are great because they are relaxed and it's for fun but people expect more for their money and want a shiny full time school which is barely economical to run without flying every second possible and paying instructors next to nothing for every hour they fly. There's a balance of course but some stuff has to give. Clubs also often suffer from inevitable "committee breakdown" hard to avoid.
The things that are free however, like treating your customers properly, calling them if you want to move their slot/ talk about cancellation giving a reasonable brief, a warm welcome and free tea and coffee are a bloody good start.
It's not that hard to do the free stuff but it's hard to hire and keep the people that understand it.