Difficult to answer this one.
Financially it's a massive step. The 24-70 is expensive, but there's good reason for that.
It's worth thinking about the DX/FX issue here too, but that shouldn't put you off buying the lens if you decide to do so.
The biggest advantage of upgrading this lens would be the 24-70mm range over the fixed 50mm.
Ultimately it's down to you to decide, bearing I'm mind the finances, and what you need it for.
I have the 24-105 f4 and 50mm f1.4 and wouldn't part with the 1.4. Will parting with your 50mm for what you'll get 2nd hand be a deal breaker on the 24-70. Perhaps hold off selling it until you have had the chance to see if the new addition fills that gap.
It all depends on the type of photography you do.
I had the Canon 23-70 f/2.8 the 50 mm was a f/1.8. Unlike CR3Snapper I did very little low light photography, so the 50 mm was rarely used, In the end I got plain fed-up of carrying around, so I sold it.