How can I tell if I have simplified my talk too much?
I definitely hear where you are coming from.

In my modest opinion, a good conference talk is not necessarily the one that lets me understand the technical contribution (I can read the paper for that), but the one that lets me understand


The importance and/or hardness of the problem studied
What were the key new ideas
Why they worked and when can I expect them to work 


If I got this from the talk, I may be able to recall the result or the technique in the future when I have a need for it.

Of course I am not saying there should be no technical detail, the key idea may be the way a theorem was proved, but I believe any technical content should not be gratuitous.