Short answer, no.
The memory allocation is what is needed to run the mapsize you are running. It will increase over the run of an individual game to account for additional ships, improvements, starbases, etc. If you forced it to allocate more memory somehow, there would be nothing for that memory to do.
CPU usage mystifies me. I understand the game is threaded and supposedly distributing load across however many cores/threads you have. I see activity on a few cores, but total usage is like you report, if that much, on my 8 core chip. My only conclusion is that AI factions doing their "Thinking" during your turn's idle cycles is somewhat of a myth. I certainly cannot demonstrate to my satisfaction that there is anything significant happening along those lines.
My question becomes this: If I walk away from the game for an hour, will the AI be doing any kind of deep dive analysis and make a more informed decision? Or, is it effectively wasting time just like every other 4X game? If anyone could speak to that, I would be very interested. I have always thought it was the former, but I couldn't prove it to you if I had to.