Does giving an easily-understood talk make the audience think you did something simple? Alice and Bob both go to a conference. Alice gives a great talk, and most people understood it. Bob gives a much more technical talk filled with jargon which almost everyone failed to understand. Do people walk out of the talk thinking Alice must've done something simple while Bob did something profound?

I get the feeling that this happens - after all given two concepts, one which I understand and the other which I don't, it's intuitive that the one I understand is the simpler one. It also feels like the easier-understood the talk is, the more questions Alice receives that aren't directly related to her work. For example I once attended a talk where the speaker talked about aggregating samples of the sky, and someone asked "why do you use square samples? Why not circles or triangles?". This kind of non-specialist question is obviously hard to see coming, and the you-either-know-it-or-you-don't result is uncomfortable. 

On the other hand, if it's indeed true that giving easily-understood talks makes people think you did something simple, it would imply that giving comprehensible talks is a bad thing. That not only sounds silly, it's also counterproductive.
I will tell you what I've observed in Math.  Similar to what Jordan Ellenberg says in How not to be wrong, one can think of depth and technicality as two orthogonal axes, so one has 4 rough categories of results:


Deep and simple (technically easy)
Deep and hard/technical
Shallow and simple
Shallow (unimportant) and technical


Some people like things that are more technical and some people like things are simple, but deep.  For instance, Atle Selberg thought that the most profound ideas in math are simple and said all of his ideas were simple ones.

Correspondingly some people are more easily impressed by technical talks and some people are more easily impressed by simple talks.  So my answer to:


  Do people walk out of the talk thinking Alice must've done something simple while Bob did something profound?


would be, while it of course depends on the audience, I think this depends largely on the talk.  If you can explain a simple idea that lets you solve long-standing open problems, I think most people will agree this is deep.  However if your talk doesn't make it clear you're solving long-standing open problems, then people will be unsure.  And you certainly want to avoid giving a talk that is shallow and simple, as no one will be impressed.

I myself generally prefer (giving and listening to) understandable talks, and here are a couple other pieces of advice:


Even if you don't want to present technicalities, make it clear to the audience that technicalities are present, and maybe make a few comments to the experts as to how you handle them.
What may seem simple to you, who have been thinking about these things for months or years, may not seem simple to others.  I've many times given talks and worried that it was too simple for the experts in the audience, and found out later that many of them didn't completely understand what I said beyond the introductory material.