Does it make sense to upgrade my set up to 4K from a (Canon) 70D set up?
It all boils down to "Do you need it"

If you are shooting corp promos and your clients keep asking or are insisting on 4K then Yes you can look into it as you can justify the purchase as the work is going to pay for it in the end.

If it is just an odd job here and there that they want 4K then hire one as it will be much cheaper at £££/$$$ for a day or two compared to £££££/$$$$$ plus upgrading cards and all your other kit to compliment the new camera.

I had the same thought but only upgraded to a Canon C100 from my Canon 7D and didnt have to upgrade much else but did get rid of a few obstacles as well.

Put the money back into some decent glass and or upgrade other elements which could make your productions better, ie Audio, Lighting, Tripods, Lenses etc camera bodies you can swap and change but good accessories will last the test of time.