Answered your own questions:
I have planted two coreopsis grandiflora "early sunrise" in my flowerbed this year...they were looking so good, but now the new buds seem to be dieing before the bloom...Anyone know what I am doing wrong? Should I be cutting back old blooms? YES Coreopsis definitely responds well to deadheading and quits blooming if you don't do it. The base of the plant looks like it is turning brown. Could it be from excessive rain we have gotten this summer? YES Coreopsis is a desert plant, very drought tolerant, does not like all this rain we've been having. Don't mulch around it, be sure your soil is very well draining, maybe even mix a little sand/ vermiculite/ gravel into the soil around it, to make it drain faster.