I'd go with Joe on the pump issue. To upgrade you would need new internal plumbing, you'd need new solution hoses and new valves on all your tools.
The vac issue isn't quite so straight forward. As Joe says, forget 3 vacs. But a local colleague has a Prochem machine (I don't know which one) He has recently upgraded the vacs with slightly more powerful versions. It was quite easy to do but you will need to speak to Prochem about your particular machine.
The performance of your clean can be greatly improved with your existing machine of you were to step up to high quality agitation. Something like an Envirodri or Prochem TM4 will make your clean, and especially the rinse, so much easier. You'll use less water and leave the carpets drier. For me, this would take priority over an extractor and would still be used regardless of how good an extractor you were to have.
Safe and happy cleaning
The Ken