I would do one sink. Unless you are planning on having a permanent couple live in your guest room, the second sink is a waste and you will have to clean two sinks all the time.

Thank you for your advice. That was my original thought, but then I was taken by the comments related to children sharing a bath and appreciating 2 sinks. My question includes eventual resale considerations.

I' don't know what part of the country you are writing from, but there are so many other factors with young families like school district, number of bedrooms and bathrooms, I don't think it would be a selling point. I think you should enjoy your home now and when you are ready to sell buyers are more interested in a clean move in condition home.