For the specific example, would it work to say there is a big burst of elven innovation before most of the race settles into new habits and innovation slows down again?

Another issue with the "limited new ideas per lifetime," is that a longer lived race means the old guard lives longer when everyone else switches to newer techniques. So you'd have a lot more old coots who used to be at the top of their field but no longer hold sway because everyone else has updated their thinking but they don't have the anima to make new discoveries in their own field. They're stuck in a rut unable to move forward, which would kind of kneecap advancement in research and development.