Resaving is not a problem because you will do it anyway at some point, but maybe it worth mentioning somewhere that the project structure have changed and it need to be resaved to improve loading time. But if it could be solved, it would be good.
If dynamic arming cause so big CPU difference maybe it makes sense to split this option for hardware and software sources.
Also 99% using this option I don't really need to record immediately after arming. For example I listen to my track from beginning, and at some point I understand that I want to record guitar. I don't want to stop playing right at this moment, but I want immediately arm track, or add new track and arm it. And if arm button is completely disabled it is really frustrating. I need to arm it, but I won't press record button right at this moment, I will listen some more, and then stop and begin to record from begging. And this is 99% of my using of dynamic arming really. So if there would be option that just allow to switch on arm for future recording after stop, I will be happy with it.