Yeah, if the 970 cost 200 then I would not do it. But 150 is not a bad price for one of the most popular GPUs in the world.
Have you considered a 1060 6gb? They are very similar in performance to a 980 and their prices have come down. You can get a decent 1060 in the US for $260 which is not much more than the price for your 980. The 2 extra gb of VRAM may also come in handy. It also consumes a lot less power than the 980. It would be a new card and you wont have to worry about the warranty ending as the 980 has been out for 3 years.
As for future proofing, you cant buy a 3 year old card and reasonably expect to be future proofing. 3 years is a long time in Video Card years. lol With that being said, the 980 is a good card, but I think I would rather have a 1060 for $30.