What do you like about the look of walnut? We put in hickory floors and I don't know why anyone puts in anything else! They are extremely durable and I noticed them in a variance of colors.

Not sure how to explain what I like about it. For one, it doesn't have very many knots and is very "clean". I also like the brown tone of walnut, not too dark or too light. And the color is consistent throughout.

Mesquite.

http://mesquitehardwoodflooring.com/engineeredmesquite.html

I agree with Unique Wood Floors. Get a walnut with some distressing already in it, that way the wear is camouflaged. You're right, there is nothing quite like walnut.
Here is a handscraped walnut by Ernest Hemingway Floors:

Acacia is the only thing that even comes remotely close in grain.

Let me ask a different but related question. If I'm only putting walnut in the bedrooms, is durability as much of a concern? Bedroom is kind of a high traffic area but probably doesn't experience as much stress as other parts of the house.

My decor is modern so I'm afraid putting distressed floors in won't look right. And, to be honest, I'm not really a fan of the distressed look.

I'd only be putting the walnut in the master bedroom, guest bedroom and kids' room (when I have them). Does walnut hold up pretty well in bedrooms or is it impossible to make that kind of generalization?

And another tangential question. When I was planning to put wood floors throughout the house, I insisted on a 4mm wear layer to get maximum longevity. But that requirement severely limited my options. Now that I'm only considering it for the bedrooms is 4mm overkill? Can I safely lower my standards?

You're obviously looking at engineered, correct?

Correct.

American walnut is very soft. It all depends on the lifestyle. It's one of the softest domestic hardwoods available. A 4mm will allow you to refinish a couple times. I wouldn't go with anything too much thinner than that. Did you try Vintage brand or Shamrock brand? Also, maybe Owens or Wickham. You should have some luck with those. Could you do a solid hardwood? Chelsea Plank Flooring has a couple of walnuts.

You know, originally I was only considering engineered wood because I was going to use it everywhere, and on the first floor the floor will be going over cement so solid wood was not an option. However, if I only put real wood upstairs in the bedrooms then I can use solid hardwood. So it is an option.

Since I haven't shopped it I have no idea how the prices of solid wood floors compare to engineered wood. I imagine it is considerably more?

Would a solid wood walnut hold up to wear better than engineered walnut? I'm guessing not, it's probably no harder but will just allow me to renew it more often.

Solid wood or not, I would prefer to have a low maintenance wood floor. I'd like the ability to refresh the floor more as an insurance policy but would rather never have to do it, or do it very infrequently.

Not necessarily more or less expensive. Depends on the brand and the grade of walnut. The brands I mentioned above are very cost friendly maybe with the exception of Vintage. Go for something with a medium sheen. The construction won't really have an effect on the durability, you're right. The finish is what will show the wear. Call around to some local retailers and ask for the brands I mentioned. See what you think. Prices will be all over the map, and probably kind of high. Walnut isn't cheap. However in most cases price reflects quality. Where are you located?

Here are some links you may like, all EXCEPTIONAL products, most made domestically or in Canada:

http://www.shamrockplankflooring.com/

https://www.quanex.com/Products/Residential/Wood-Flooring/Prefinished-Flooring.aspx

http://www.wickhamhardwood.com/

http://www.plankflooring.com/

http://www.seasonsflooring.com/

I would put any of these products in my own home. Wear and durability will be somewhat similar as the density of american walnut is the main issue. You could use "Asian Walnut" or Acacia, but it's going to be Chinese, and not as consistent in terms of manufacturing. Also much shorter boards, as it is I believe technically more of a bush.
I wouldn't personally go that way unless the budget constrains you.

I agree with Unique and Legacy on going with Acaica. Walnut looks amazing, but it really isn't a good choice fro a floor.

A new one on the block to look at is Australian Eucalyptus. It's considerably harder than Acacia and has a very jazzed up grain. We can't keep the stuff in stock - amazing floor!