I wish I could offer more insight - I think you raise an interesting question here. I know in my kid's bathroom, they 60" vanity with 2 sinks, and there is a wall on either side of the vanity which makes is less roomy. It sounds like that is your layout as well. Yes it would be better if there were more counterspace, but it is certainly usable like that. Generally , I think that the 2 sinks would appeal to more people, even if in reality one would really suffice. It's the kind of thing that I think might not be rational, because counterspace in my view would be preferable and really, how often do the 2 people use the sink at the same time (in my house hardly ever). I would be interested to see what others way in with. Another question I would raise is what is "typical" or "expected" in comparable homes in your area.
(and I love your description of the obnoxious non-standard 1/2"!).

I would seriously consider going with the 2 sinks. We only have one and I find it annoying becasue we are in there at the same time and it would be nice to have the extra sink. I also think re-sale wise the 2 sinks will be more appealing. If you do undermount sinks and keep the faucets simple - I think you might find you have more than enough counter space. Just my 2 cents....

I have a simailar situation in my hall bath and I have decided to so one longer trough sink with 2 faucets since I have 2 kids. It seems to accomplish both needs. I found a cool one that is 40 inches long that sits on top of the counter. I haven't decided on the size of the vanity pieces underneath yet so this is very preliminary.

Here is a link that might be useful: trough sink

Here is another one although I can't find the more traditional one I originally found that had an overflow. With 2 kids, I can't risk a flood!

Here is a link that might be useful: another long sink with 2 faucets

We only wanted 1 sink but as a compromise decided to rough-in for a 2nd sink. That way if we or a future buyer ever want to add a second sink the plumbing will be there even if the sink itself is not. (This is my first post after months of lurking and learning!)

We went with a 48" vanity and a single sink and left room for a towel bar on the end and the wastebasket. Also we have a holder for hair blower and curling iron and the cords are draped in this space.

Here's a vote for 2 sinks. Our master bath has one sink and it's annoying to my DH when I'm at the sink brushing my teeth and he's waiting to wash his hands. Our main family bath also had one sink with a 50" width old custom vanity and when we remodeled we took part of a closet to allow for a 60" vanity plumbed for 2 sinks. Counter space is sufficient with the 2 undermount sinks (we don't like countertop clutter anyway)and we're glad we went to the expense. Good luck!

After much conferring and also reading the input of people on another home site, I think I've come to a conclusion!

I'm going to put in one sink centered in the vanity and leave the area plumbed for two. When I sell the place I can point out that it can be converted to a dual sink vanity by replacing the top. That's a minor job, really.

I saw a vessel at Home Depot tonight that's an amber color glass with a textured pattern on the outside for $69. There was a clear one for $99...odd. Amber is a nice, warm color that I've used in some of the lighting in the halls and living room. I'm not sure if that would be overkill, though, because the shower will be slate. Possibly too much 'dark'.

I think vessels are neat, but I think they give the illusion of less counter space because they hide the area around them. Not to mention the need for a tall faucet, which frustrate me because I want a nice oil rubbed bronze finish. Tall faucets seem to be limited, still.

Thank you for all the comments! Everyone had some very valid points to make. My mind is at ease, finally.