All strains of CAE can probably cause symptomatic disease, many herds are tiny and don't have a statistic size to show it in all herds. And then it is likely intercorrelated with individual herd management as well. Finally, CAE is inherently a very rapidly changing virus so you can't feel too safe having a strain on your property as it could always become a more virulent type, really.
Personally I don't want CAE in my herd. It is VERY simple to test for and eliminate, and there is not a lot of good reason to buy the problem IMO, because there are plenty of affordable, negative, healthy animals out there when buying that very few animals are worth buying positive if your goal is to breed. Even if you are just milking the dam, she must still be bred yearly to produce milk. If you tested a mature animal and found out it was positive, there ARE ways to manage the disease depending on your goals, but IMO there are not a lot of good reasons to bring it in. I think with a wee bit of patience you could find an equally good or better animal, so why buy a potential problem?
If a doeling is being fed positive raw milk, she is likely positive. If she is being fed PASTEURIZED CAE positive milk, she MAY not be infected but be seropositive until the antibodies to the dead virus have been eliminated from her body. If weaned around 8-12 weeks as common, you can often have those animals test negative at 6 months. It is NOT suggested to test them younger than 6 months because killed virus milk can still contained passive immunity as well as the fact that a dead virus can also cause an animal to produce antibodies (which is how vaccines work too, but incidentally CAE antibodies are not protective) - and it takes a while for the body to downshift production of CAE antibodies after the last exposure (last feeding of positive, pasteurized milk).