I've fished it a couple of times during the last ten years and have done o k. I've always fished it during the cooler months. Fishing Creek certain has come a long way since the DH area at Grassmere Park is gone. When I've fished there it's been pretty good even during the summer, the 2 branches actually sink (think Substrate) during low flows down near route 118. Looking over the bridge and driving around that area, reveals quite a few springs where the water comes back up and trout in the springs.
The headwaters of both branches seem to be very infertile though, especially the EB, so the population there isn't quite what it is in the WB. The tribs can be good and some of the tribs to other tribs of Fishing Creek appear to have good fishing, but I haven't fished them yet. If you want more info, PM me.