This is a big point of contention for many brewers. If you are on a budget and looking for ways to save money - brass is the way to go. I don't buy in to a lot of the hype about metals "leaching" from brass into the wort. There is a small concern about surface lead, but that is remedied by a short soak in a 2 parts vinegar to 1 part hydrogen peroxide solution. I would avoid brass contact in post fermented beer, but for mashing and boiling, I think brass is fine. You certainly can't hurt anything by going to stainless, but, I wouldn't spend money on stainless unless the rest of your brewery has all the other things you want. Here are the things I would put ahead of stainless valves and fittings:
1) Keg fridge and beer faucets
2) Fermentation temperature control
3) Stir plate and flask for yeast starters
4) Glass (or stainless) fermentation vessels (dump the plastic!)
If you have the above, or just aren't interested in the above, then perhaps going to stainless makes sense. If you contact me directly, I can probably get you anything you need at a good price (
[email protected]).
Regarding SS QD's, you will spend a fortune here. There are high quality plastic QD's that are much cheaper and will stand up to just about any temperature in the brewing process. If you are careful, you can make these last for years and take the money you save and put it somewhere else in the brewery.
Prosit!