TL;DR for nothing Crypt.
Normal gnome coins - Useless... unless you plan to get level 15 rings which are still good at 16; but I had necro+stun ring anyway.
Valuable gnome coins - If you saved chaotic tokens at level 11-15 they are useless too because you know how "easy" you can get helmets level 15 therefore making valuable gnome coins useless... But if you want to do another set after being level 16, those might turn useful because there are no chaotic tokens at level 16-19 anymore (And this is a bit stupid in my opinion). But -- Level 20 will come in COM too, so I'm not even sure if you really need to save them - You cannot make a level 20 purple helmet through valuable gnome coins, at least in RU.
Quicksilver - I still have 60.000 qs and I am too lazy to go magmaland to open runes... I didn't find a purpose yet other than going to open red runes. But anyway I would do it only to gain little money - That I can do through hunting tbh.
Maybe there are other uses I forgot or I didn't think about - but definitively farming coins/qs is not worth your time at this level. Level 16+ players get jewellery items through shaiss substances system, so by doing instances and eshu decks + using bowls.