Priced up the parts to update my PC, out of interest. If I stick with the same case and GPU, it's around Β£500 for something that'll last me another 4-5 years, at least. If I stretch to 600ish I can get a bigger case/mobo, which will give me more expansion options (and probably better cooling).
Graphics would get upgraded next year if necessary. WoW isn't particularly demanding, even at 4K.
I'm tempted, but it's all low priority right now.