I'm stepping in late in the game.
So, I guess it all depends on three things:
1. Location
2. Location
3. Location
Urban areas, 15-20K plus in populations.. Then yes, the theory of the volunteer service should be phased out, and people should be paid to staff 24/7. The actual people who do it are most likely no different than you or I.
Rural areas 5-12K plus in populations.. Guess it depends on the call volume and response statistics. The local EMS team here has some kick ass rigs. Everyone had a hurst tool, ladder, SCBA, TIC & Rope gear. It's own little self supporting rescue. They staff two of the four rigs 24/7, with no paid crews. Of course their call volume and the tax base doesn't warrant having more than one paid shift. So they also run a MICU.
Less than 5K. Don't see any problem with that, as long as they respond in a reasonable amount of time. i.e. less than six minutes.