I think if you need to be payed to be loyal to Starfleet/The Federation, that kinda is a deal breaker given the philosophy of personal growth and societal enrichment.
Perhaps, but I’m sure they are also aware of the cultures of other species, and having those species in their fleet is still a vital asset for dealing with disputes against or with those species. I’m sure plenty of species don’t mind like vulkans or Klingons, but there are other species that find their collective value in material wealth.
I would suspect that the real draw to working with Starfleet for non-federation personnel isn’t any concept of wages, but a comprehensive benefits package. Presumably Starfleet membership confers some level of personal federation membership, possibly for both you and your immediate family, which may mean that you get to move your loved ones to a mostly-utopic federation world.