I don't know much about UA. I have a couple of their t-shirts and they are okay, just okay though, not great. Their material doesn't wick moisture as well as some others and that is the key to a good base layer in any weather I experience here in VT.
I've had nothing but the best of luck with Patagonia Capilene. No other brand I've used works as well, sounds kind of snotty but it is true. I've tried a ton of brands and in the end it was "penny wise and pound foolish". Spend the money on a good set of capilene and you won't regret it.
Yes, wool is a good insulator, but it is not a base layer. You need a wicking layer to get the moisture away from your skin. Wool gets wet and continues to insulate but it stays wet. You don't want that against your skin in really cold weather. I have a smartwool shirt that I use as a second insulating layer when it cools off. Even then, I've found out fleece works better most of the time.
Here in VT I always use a base layer and add layers (insulating, breathable, wind stopping) as necessary over that - unless it is the middle of summer - but even than I have capilene T-shirts.
Capilene comes in a variety of "weights" the light stuff is great in warm weather and up to pretty cool stuff. You might want to spring for expedition weight if you go out in really cool stuff.
I think the key is to treat hunting like any other outdoor activity and use technical clothing to its best advantage. The weather doesn't care what you are doing and layering with good technical fabrics makes sense whether you are mountain climbing or duck hunting.
Charlie
PS. Added - If you want to get rid of the stink in polypro clothing use a detergent called Techwash by Nikwash. It is expensive, but you only use a little each time. The stuff also helps restore water repellency on DWR fabrics.
PPS. Also, there are no better socks than Smartwool.
PPPS. Do I sound like an advertisement yet? Maybe I can get a job in a hunting rag .... "then I took my Remongton model 700 SSP rifle, coated in non-reflective Stealthtech coating, and aimed my 3-9x40 Swarovski scope at the trophy buck provided by Buckslayer Outfitters and shot it with a Wincester Supreme bullet coated in Lubalox...." LOL