Seems that some gardeners are able to control it (live with it) and some not.

I haven't had it in long-lived old cultivars; namely, 'Magnus' and 'White Swan', but have had it in newer ones (including 'Hot Papaya').

Perhaps the older ones and the species are more resistant.

I definitely keep an eye out for any infected blooms when buying any new echs at a nursery.... if a plant or two show signs then I just skip the lot. But this is never fool proof since they might not be blooming yet and I have brought them home I new plants. The few nurseryman I have talked to note that they are getting plants already infected from the growers... Why they aren't returning them beats me.
In the end it's no more of an issue that you have to deal with on other perennials or veggies in the garden... But I am quite bias to echs.

I'm no expert, but would think if the plant is infected with aster yellows it's in the whole plant and picking blooms will not help.... It may help with mites though, and I would pick them anyway just because they bug me (no pun intended)

In the former case, only the flower is affected in an otherwise healthy plant. Also some of the original flower colour usually remains.

Re above: as has been said, by the time the flower damage is apparent, the mite is already established in the plant.

Coneflower rosette mites are microscopic, their population builds up to very large number in a single flower, they apparently spread by wafting from leaf surfaces, in the wind, and they overwinter as adult females in plant debris.

It's very informative to read NM's comments.

As said, my 'Magnus', "White Swan' and species have never been affected. It seems interesting that the only affected coneflowers I've had, have been newer cultivars that were purchased within the last ten years. Maybe it's when the plants were purchased as much as what cultivars they were.

NM, re the retailers (and other parts of the horticultural industry) it's all about the money. But I bet you knew that!