I think you can safely assume that if the system boots with the new memory installed then it is using that memory.
Performance far more likely to be determined by the speed of the database and DSP ie the processor and the system storage (the SSD card). It won’t be determined, significantly, by RAM size or the speed of the disk holding the music files. I assume that Roon Labs have designed the system software to function with the given RAM, so I am not sure you would see any performance improvement.
How do you know when ROCK is running out of system resources? Both CPU and/or RAM?
I have nearly 6.5K albums, so 85K tracks on NUC5i3 with 8GB RAM - this could go to 16GB, but would it make a difference?
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.
RAM upgrade (in type or capacity) will have no effect on sound quality. Only thing happening when the Nucleus run out of memory is that it crashes (restarts). Trust me on this one; I have experienced it. Also see comment from the Roon team regarding this.
We humans are a weird specie, and our mind plays tricks on us. We are affected by other senses than hearing, and we are biased regarding expectations.