I think the single mirrors definitely are more decorative and you then have the option to add an additional element in way of the frame you chose. You may also have room to add a single sconce between the mirrors for an added level of light or some other decorative item. Maybe have space for a counter garage. I can't help you off hand on the mirror sizes. Mine are packed in the garage of the other house. To get an idea go to the gallery of the decorating forum and look up the bathroom eye candy thread and there are literally hundreds of photo's. You should be able to get some ideas from there by looking at idividual mirrors and how their size relates to the vanity/bowl size. You can also google vanities with matching mirrors and that will give you specific sizes. Good luck.

Many thanks to everybody who answered, you have all been very helpful in clarifying my very muddled thoughts. Here is a hopefully clearer description of the situation: The house is a 50's ranch style, with 3 bedrooms and a hall bath (4.5x8.5 ft) clustered on one side of the house, and the kitchen, office/den and another hall bath (4x9 ft) on the other side of the house, with a great room in the middle. We plan to stay in this house as long as we can, but we are in this city for my husband's work, and if something happens (although unlikely with his kind of job), we know we'll have to move somewhere else; therefore, we'd like to make updates to the house while keeping resale in mind. Our (excellent) realtor said that for resale we should have an ensuite. After reading the comments, I have to clarify with him if he thinks a lack of ensuite will narrow down the market significantly, or if we 'simply' would not get the best price for the house. Most houses in the area are old (in the whole city actually), and we saw plenty without ensuites. We saw two of the neighbors' houses, and they did not have ensuites. This is what we considered: 1. Redo the bathrooms with the existing footprint (not that we have room to change anything inside), but we can go far into making them pretty, 2. Add a door from the master bedroom to the hall bath next to it, and close access from the hall. This I think would be a bad idea, not only because the people in the other two bedrooms will have to go across the house to the other bathroom, but also because the master bedroom will end up with windows on two walls, three closets on another, and two doors on the fourth side. Not restful. 3. Add another bathroom next to the master bedroom where the closets are, with one closet door transformed into a bathroom door. This bathroom would be 4.5x12 ft, although it could go to 5x12 if need be (but no more, because we'll hit a big window), which will have a shower but no bathtub. We talked to a professional who said it will fit fine with the caveat that the toilet will likely be the first thing you see in front of the door because of the current clearance requirements. 4. Build an addition. This again I think would be a very bad idea, since it would be blindingly expensive and the house is already on the higher side of square footage for the surrounding area. We will of course fix everything that is broken. The interior doors are the original 50s doors, hollow core dark wood look with lots of scuffs and holes, and they were cut short to fit the now non-existent carpet, so I would qualify changing them as fixing what is broken (and they bug me every time I look at them... ). The windows are a perk; we are still divided on those. I tend toward option 1, while my husband is going for option 3, although he agrees we do not need another bathroom. The reason I feel ill equipped to make this decision is that I'm originally from Europe, and even after so many years here I feel mildly perplexed about the North American love affair with bathrooms. Our previous rental was built in the last ten years and had a huge ensuite which I didn't like. I found it hard to keep as clean as I thought it should be, and it was so large I felt as if I was doing my business in public. Given the bathroom pictures on Houzz, I'm clearly in a minority. Your comments help ensure that I don't miss anything that might otherwise be obvious, so thanks again. And extra thanks to whoever makes it to the end of this post...

I remember in my first house, I made a recessed closed niche all along the vanity between the faucet and the mirror. I found it really useful, I just wish I could find a better option than sliding doors to access the inside. I don't know, if 30 years later there would be a better option ... maybe you can make that recessed space higher than the faucet and have a pressure button latch that is hidden at the back of the door (sorry, I am missing some english vocabulary, hopefully you understand what I mean).

Agree with Design Girl. Seems like a waste to cover up your wall tile with a "slab" of mirror. Arteriors has some more interesting mirrors. Not cheap, but I've gotten better prices locally. https://www.arteriorshome.com/shop/wall/mirrors Lots of mirrors at Uttermost too. https://www.uttermost.com/Mirrors-View-All/