I bought a minimal amount of 3rd party stuff during 3E, mostly wholly separate games (AU/AE, M&M, Spycraft, etc.) but I think my answer is yes. I'm so disappointed by the GSL, that despite my excellent experiences with 4E so far, I may abandon it.
I think all of you who are saying you will not be impacted by an expected lack of 3pp support are missing a key fact. You may not have bought much of it (or any), but the mere fact that the OGL existed and that smaller publishers rose up around it gave us some of the best design and development minds of the last ten years. Mike Mearls & Keith Baker both spring to mind as a clear examples of people who benefitted strongly from the open-gaming paradigm because it gave their abilities a chance to shine. As a result, they both wound up working for WotC. Will the Mearls and Bakers of the next ten years simply go undetected? It's certainly more probable. What about the guys at Goodman and Necromancer and Green Ronin, who may never have "made it to the top" in Renton, but whose excellent work certainly influenced the direction and overall quality of the games we got to play in positive ways, if only by inspiring the guys at WotC.
I think before we get around to 5E, we'll all miss that whether we realize it or not.