A symptom of needing RAM is a crash, nothing else. Roon OS does not have a swap file or do anything else memory based on the SSD. It’s all in RAM.
If you added RAM, you shouldn’t feel any changes other than “its not crashing anymore”.
If you weren’t crashing before, adding RAM will not cause your system to speed up (Nucleus doesn’t swap), and should have zero other impact other than growth potential. Roon doesn’t use more RAM just because it has access to it.