Ball Valves - SS or Not?

I'm going to be picking up 2 kegs tonight for conversion to a HLT and boil kettle. I'm starting to think about fittings I would like to put into them. I'm thinking valves and thermometers on both and a possible sight glass on the HLT.

1st question: What is the advantage of going with SS over brass valves? I'm thinking of picking up the SS weldless setup at Bargain Fittings but I'm not sure if the extra cost provides any real benefit.
2nd: Is a 3 piece valve worth the extra cost? Bargain fittings doesn't offer this option but I have seen them around.
3rd: Anyone have any good suggestion on a weldless thermometer? I was thinking of these.

Thanks!

I think stainless and 3 piece set-ups are PURE luxury. They really add no value to a homebrewer. If you were going to be using the system for commercial level production, you might be able to make a case for stainless being something more than just extra-shiny.

Keep in mind that I have 2 three-piece valves that came with my conical. Having used and cleaned them several times, there is no way in hell I'd spend the extra money to change over my boil kettle or HLT.

So, If you have money that's burning a hole in your pocket; go get em! If you just want something that will do the job well - don't bother.

The only case I have to make for SS over brass is the SWMBO("lead-free brass still has lead"). She works with the water utility and gave me enough grief (and the go ahead to spend the $$) that I just went SS on all my valves.

I got brass for HLT, and 3-piece SS for MLT and Boil Kettle (since they see sticky wort)