Couldn't agree more. Innovations in any given branch, especially science, generally follow a recurring sequence of:
1) a quantum breakthrough -- a novel discovery of / insight into / use of a hitherto unknown or little understood phenomenon.
2) frenetic exploration and/or development of the nascent field; usually follows a near-exponential curve
3) a plateau of incremental refinements till the field reaches relative maturity ...till the next big one.
It seems plausible, given that there is a finite set of distinct essential phenomena in our world, that each iteration of the cycle gets progressively longer and harder, as our knowledge-base of a specific domain increases in depth and complexity.
This would probably explain the apparent slowing down of innovation, if one merely goes by the rather crude metric of the rate of tangible and immediately useful contraptions being spawned.