I still buy thread from JoAnn's, but I wait for the sale. I don't worry about the color of the thread as I buy mostly neutral gray or beige. Saves a lot of time and those two colors blend with almost all other colors, except black of course.
I think the fabric has become thinner regardless of whether of I buying from JoAnn's or my LQS. For those of you who have older stashes, it might be interesting to wash 1 yard of new fabric and 1 yard of old fabric and compare the weight and fraying. Might be interesting data collection and give us a basis for whether it actually is thinner.