I currently have and have had quite a few wool pieces, tops mainly, but also tights and underwear from Smartwool, Icebreaker and Minus 33. I have worn mine both for day hiking and thru hiking. Here are my observations.
Long sleeve tops, 200 weight, which is probably the mid-weight. I have both Smartwool and Icebreaker in the quarter zip style. I alternate them both for day hikes and the Smartwool came along for the LT, AT and other backpacking trips. I machine wash and air dry these two pieces and they've held up very well. The Smartwool is probably 4 or 5 years old.
Short sleeve tops, 150 weight, in Icebreaker these would be the Tech-lite tees. For thru-hiking, I was getting about 700-800 miles out of a shirt. I only had one shirt and wore it just about 24/7, except when I did laundry. Hence, the short life span. I did hike with a guy who wore the same Icebreaker from Springer to Dalton, MA and then it really was done and trashed it there. The shirts would get thin on the shoulder and back where the pack would rub and eventually get a hole and then it was done. These shirts I machine wash and dry and they seem to be fine. I had one Minus 33 and it got a hole rather quickly, and I was only day hiking with it. I have not bought another one of those.
The tights, I've had both the 150 and 200 weight and the 150's were fragile. I thought they were a bit thin for what I put them through hiking, they got holes easily. The 200 weight are going strong and are my "light tights" for winter hiking and thru-hiking/backpacking when the temps are cooler. I've had them 3 or 4 winter seasons. These get machine washed and dried. They seem to bag out at the knees and elsewhere, meaning they stretch out with wear, but rebound after washing.
Underwear, at least for the women, the Icebreaker underwear I found to fragile for thru-hiking, but okay for dayhiking. The Icebreaker bras are excellent, I've had several and used the same one for the entire AT and still wore it afterward, same cleaning routine on the trail as the long distance shirts (laundry once a week or so). Eventually the edges frayed and the elastic gave out, but not the main fabric, so it had to go.
All that said, polypro and the like are definitely more durable and preferable depending on the activity. If I am going to be bushwhacking, I will not wear my long sleeve wool tops, I will go with an old red EMS polypro quarter zip. Thru-hiking, I expect things to wear out, they just do if you wear the same shirt day after day. We did find that the wool was less stinky for continuous wear than any synthetic. I say "less" because thru-hiker funk is pretty much thru-hiker funk - it is all bad and nothing short of incinerating the garment will get rid of the smell.