Even in large scenarios, I have never seen Commmand use a lot of RAM. I ran it on a 4Gb RAM Surface Pro for years with no issues and it never seeming to use all the RAM available. Of course it was slower than my laptop with 8Gb of RAM, but it had a much slower CPU.
Back when Command first came out, I tested it on my laptop with both a HD and and SSD. The SSD only seemed to make a difference on start up, scenario load, and accessing the database viewer. There might have also been an impact on menus as well. But if I left the game running on its own, the performance was almost equal between SSD and HD. Where the SSD and HD, and RAM for that matter, made a big difference was if I was doing anything else like email while Command was running.
I tried using a RAM disk on a work computer that had 24 Gb of RAM. It was just not worth the effort. It took a long time to load and I saw almost not performance change. I also had issues with pictures in the database. Again, wasn't worth the effort.
So my conclusion has not changed much over the years. Command is CPU-intensive and its performance is very much CPU-locked. You can nibble at the edges of performance with GPU, RAM, SSD, etc. But a low-end CPU will never perform as well as a high-end CPU. But you can get very playable performance with something as low-end as an i3. You just might not be able to play 3000-unit scenarios in a couple hours.