Nikon 14mm 2.8 prime vs 14-24

[PushingTin]

I currently have the Nikon 14mm 2.8 prime but using it on my D300.

I know this lens is meant for FF but I am not that happy with the corner sharpness and flare of the lens.

Will this lens perform better on the D700 than it does on my D300?

Is the 14-24 that much better that it is worth upgrading the prime?

Trying to decide if its worth upgrading the body or the lens first.

Thanks in advance