I think one of the issues is that the rate of progress is slowing as the technology matures. Today's entry level DSLRs probably have the performance that "state of the art" models had 10 or 15 years ago. The difference in image quality between a low end APS-C rebel and a full frame pro level DSLR isn't really that much for the applications that most people have. If your making poster sized prints at iso 25600 then the difference might be significant. If you're shooting for 8x10 prints at iso 100, it isn't. Recent new models tend to feature faster processors, more complex metering and AF systems, Higher resolution video (4K), more connectivity and other features not really directly connected to still image quality.
Whether you need higher image quality is a personal decision and depends on how you will be using your images. Personally I'm fine with the IQ of today's DSLRs. I'd like to see higher image quality in smaller, lighter cameras with smaller sensors. There's still room for a lot of improvement there!