You are making this way more complicated than it needs to be. All of the recommendations that have been made are good suggestions. All of your original ideas were good ideas to consider. No one has said the Vantage is "better" than the Odyssey. It is different and excels at certain things. It is smaller. But there are plenty of people who would prefer the Odyssey over the Vantage. And plenty of people prefer the Prodigy over the Summit. But for you to make that decision out of hand based on a "gut feeling" without auditioning the Vantage and the Summit would just be foolish.
The problem, as I see it, is that you want a cut-and-dried solution handed to you on a silver platter without too much work on your part. You want a better speaker, but you don't want to spend a bunch of money on it and you don't want to audition a bunch of speakers.
We can only make suggestions based on our experience. But none of that matters in the real world. If you don't manage to get out and demo some of these different speakers so you know what you are getting into and what the sound and size differences are between the Ascent and Odyssey and Prodigy and Vantage and Summit, then nothing we can say is going to help you. It is a crap shoot. You ask ten different people on this forum what their favorite Martin Logan speaker is and you will get half a dozen answers or more.
Ultimately you have to decide what you like the best and what will work best in your room and that is going to be difficult to do if you can't arrange to audition at least some of these speakers and compare them to what you have now. I am no expert in upgrading caps, but I doubt that will give you near as much of a performance boost as going to a newer speaker model.
The beauty of buying on the used market is that they will hold their value well. So if you buy Odysseys or Ascents now and decide you want to upgrade to Summits or Vantages in a couple of years, you won't lose much reselling them. Or you could end up with a speaker that you are completely happy with for the next fifteen or twenty years.