I really doubt that gridseed miners are doing anything to the prices. They cost much more per KHs than GPUs, especially now that Newegg has lowered gpu prices again. I know people are still building mining rigs as fast as they can, I'm selling thousands of usb risers a week. It has slowed down some, but a lot of people are still getting started.
I agree on the gridseed miners - I watch this carefully, but at current capital costs, they are not more cost effective. It is better to purchase cheaper GPUs and run them undervolted - I look at windows of 3-6 months of time for ROI. Gridseeds may be 6+ months ROI, and that starts to get very risky with the current BTC and alt coin climate.