I use Cokin P filters GND, ND8 & CPL. But IQ suffered somewhat when used on 17-35. So I stopped using filters. Using FX body. I was indeed thinking of selling one of them to get 24-70. But can't decide which one.
My personal opinion based on my own personal experience.
Lens choice/selection should be made with two major considerations:
1) What subject you shoot PREDOMINANTLY, i.e. what focal length and aperture are most needed to do what you do most of the time? For example, I do mostly travel scenary and landscape, and also travel portraits of people I encounter on my trips. For the former, I chose the Nikon AF-S 14-24/f2.8 to be able to really capture wide vista views, and the latter, I chose AF-S 70-200/f2.8 VRII to be able to zoom in close for the portraits without having to be too physically near the subject as to become intrusive. For general walk about, I have the AF-S 50mm/f1.4G on my FF body most of the time.
2) When buying/deciding on a lens, think also a little whether you're building a 'system' with good focal length range and good lens speed. Hence my choice of lens as explained in 1) above.
3) On trip when I have more time at specific locations, I might bring along 4 primes instead of zooms, e.g. Zeiss ZF Distagon 25mm/f2.8, Makro Planar 50mm/f2, Makro Planar 100mm/f2 and the Nikon AF-D Micro 200mm/f4. These are on trips where I can take time to compose, manually focus, and get the really sharp shots.
But 14mm vs 17mm very hard to ignore. 3mm on the wide end is a very big difference in view angle. So in the end, you have to ask yourself if you really need that wideness. If you shoot only 17mm and tighter, 14-24 will not make sense.