I've pretty much always had a dishwasher, and would never, ever be without one.
I'm in the NW too, so very soft water, and after having learnt to my cost just once: I will NEVER put salt in the diswasher again.
For some reason after years of being fine with no salt, I decided to put some salt in, from that moment on, i was finding rust spots on cultery. I never had that before, and did check it was dispensed correct and no spills/leaks etc, also made sure the machine was set to correct salt dose level etc.
This was a few years ago and have changed dishwasher twice since then, and the manuals for those two dishwashers said NOT to use salt if in soft water areas.
However, see how you go and you'll find the results you're happy with.
Oh, also agree Fairy Platinum is the best. However, I have used others and they have been fine.