Claire,
I have exact same set up as you (D500 in Aquatica) and 60mm lens (old version) and I got a +5 wet diopter from Aquatica and absolutely love that set up. +5 definitely provides significant magnification Vs just using 60mm and based on my experience so far, i would not be getting a +10 one as that one would be nearly impossible to focus i think.
I picked up a focusing trick on here - if i see a suitable subject, i firstly focus with the 60mm, then swing the wet lens in place and then the system focuses easy. If you do nto focus w/o wet diopter sometimes it hunts too much.
Also, with 60mm, you distance to subject is pretty close, so need ot be more careful with lighting and pick subjects carefully.
Here are some quick grabs - excuse the poor image quality - these are JPEGs from Ipad, did not have time to work with originals yet - but shows what is possible.



