For me, the main advantage of wool is lack of stink. I wear my merino base layer for a couple weeks of everyday riding without washing it and still no stink. However, if synthetic fabrics didn't stink after 30 min of exercise I'd use them instead. They're lighter, more durable, don't absorb as much water, and are cheaper. When it's 50 and raining I usually wear a wool baselayer and 100 weight microfleece sweater (synthetic). The dense knit of the sweater blocks a good amount of wind and sheds water pretty well. If it gets colder I add another layer in between.