I really don't know what AMD line up for GPU is next year, everything seems very uncertain. They might release navi, might release a vega rehash on 7nm, navi has been rumoured only to be 1080 level type performance. Nobody knows really.
I was going to ask what resolution you play at and it seems a 1440p. If you can be patient enough to wait and keep saving money till next year for new AMD GPU then wait by all means. But your current card is not adequate for 1440p gaming. You really need Vega56 upwards for that. I think a vega56 would last you a while yet, how many years its hard to tell but i think you should be good for the next 2 years at the very least, specially with a overclock. If you plan to keep you card for few years and insist on AMD cards then vega64 is a better buy. Inside the Vega64 thread there is OC setting without any crazy modding that gives you gtx1080oc or beats it. People are under volting them and getting excellent overclock with good power saving just buy a good card to start with.
you could sell your card and put that money towards the vega54 purchase, might get £100-£150 for it depending on whether its 4GB or 8gb that would make your vega54 purchase £250-£200 or so and next year if something out of this world gets released by AMD you can sell that and buy again. You do loose on each sale but its better than holding onto a card that will depreciate to nothing.