Like any "is lens A better than lens B" question, you'll get a lot of different answers, some useful, some not so useful.

First of all, the 55 Zeiss that you mention isn't for sale yet. They claim is is the first of a new generation of Zeiss optics for 35mm (probably not "new" in the new-to-earth meaning--I bet they are just designs from their motion picture gear--highly regarded--or scientific optics, repurposed to still photography).

I *do* own a number of the Zeiss-for-Nikon lenses and I do like them. I'm not a pixel peeper and don't do "lens testing" (quotes intentional) but the images do seem sharper, more contrasty, and just a nicer look than other lenses. I've tried a variety of Nikkors but not Sigmas or Tamrons, or any of the more obscure off brands, though I hear in many cases they are quite good.

i suspect that Zeiss's quality control process is more rigorous than Nikon's. That is to say, I've had lenses from Nikon that other's have praised that I have not had as much luck with--especially zooms--while each of my Zeiss's has been excellent. So part of what you may be paying for is simply the extra cost of more thorough testing, etc. The guy at Lens Rentals is the only one who has seen enough samples to really know...

You are also, in my experience, paying for outstanding customer service. I've had two problems with my Zeiss lenses. Both were taken care of immediately (as in, days). In one case I was sent a new lens, despite the problem being one that could easily have been repaired.

A big advantage of the Zeiss line is that they are manual focus. AF is great for many purposes but no so great for others. You'll notice that on the same focal length, the barrel of an AF lens only has to turn a little bit to go from it's minimum focus distance to infinity--I guess that makes it focus faster--less lens to turn. (As a side note, I've always wondered if that also caused more focus errors--a very slight miss would be a significant distance change for the plane of focus...) That also makes them problematic to focus in manual mode for many uses. Too hard to hit your target. Much easier to be precise with a manual focus lens (Nikkor or Zeiss) at the sacrifice of speed. The focus stays put, too. On AF lenses in MF mode I find the AF far too easy to bump. Try shooting astro images in the dark with one without taping the focus ring and you'll know what I mean. Or stitching a 24-image stitch. Whoops. Must have bumped the focus ring around image 8. Oh well. Uggh. Been there, done that.

On the other hand, I have had in some cases outstanding luck with Nikkors. I had a 28-300 Nikkor that seemed better than the average, based on what I saw on the web. Its focus (or the camera's focus) wasn't always spot on all the way out--quite frustrating--but when it was on it was surprisingly good at 300. I also have a new 300 f/4 Nikkor that is simply stunning. I read they were very good on all the forums but the one I received seems extraordinary (shooting on a D800e).

But they are a different breed. No zoom. No AF. Expensive. If those aspects don't bother you--or, indeed, if they attract you--buy one used or rent one. Renting is inexpensive, buying used is often free as you can sell it at about the same price if you buy it right.