Most homeowners have the misconception that the cost of home improvements can be recouped upon sale, when generally you are lucky to get 50-70% back.
Google this search phrase for more info on what types of improvements fare the best and worst - value of added bathroom
We had a neighbor who, after several years of unsuccessful trying, in a good housing market, was finally able to sell his house last month - his problem was he built a large and ery expensive hot tub into the master bedroom by taking room from another bedroom a couple of years ago - so there was a large hot tub in the master bedroom, plus he lost a bedroom - finally sold at less than area market price, and the new owners are going to tear it all out, barely used.
Generally, unless you are adding an upstairs bathroom where there is none now, or doing a fairly professional job as a do-it yourself project, it is very rare for a home improvement project to be recouped upon sale, and some like swimming pools can actually detract from resale value. The ones that recoup the most are adding something that is expected in the neighborhood and for that level of home, but it is blatently missing - like a garage, paved driveway, usable size kitchen, deck or patio, or fixing something that strongly detracts from the house value like a bad roof, deteriorated siding, etc. This latter mode - fixing things that are in really bad shape - is how inestors make their money - by taking the worst on the block and making it one of the best with simple, cheap repairs and enhancements.
Another reason you generally cannot recoup the cost of additions is simple math - an existing house is priced based on its replacement construction value - i.e. it is competing with equivalent new construction nearby. However, doing remodels and additions costs about 25-50% more than the equivalent item built into new construction - so you automatically, even without figuring that it is used rather than new, are at a 25-50% price disadvantage, so to get a sale you have to price it that much less than improvement cost to compete with the new construction which tends to drive the resale market values.
However, as you indicated, there IS a big difference between resale value and resale desirability - having a conservatively done upgraded kitchen, private master bath, additional upstairs or basement bathroom, large deck, landscaping where it was trashy, etc CAN interest more buyers hence move the house FASTER - just commonly does not raise sale price much. In your case, and personally having 3/2 upstairs, I believe it would certainly make it more saleable - but I still think you would only recoup maybe 50-75%, not 100% of the cost - particularly because bathrooms are high cost per square foot, relatively speaking.
One other factor is a lot of appraisal valuation and resale value is based on square footage and numbers of each type of room - so upgrading does not show up at all in the estimate, and adding a bathroom removes bedroom space so there is little net gain there UNLESS the house was short of what would be expected in the way of bathrooms.
There is a famous byline in the industry - if you take a $70,000 house and add a $30,000 upscale master bath to it (you can tell by prices that this is an old line), you do not get a $100,000 house - you have a $70,000 house with a fancy bathroom that is out of place in the neighborhood. This commonly happens with people who do a major addition - the house can become out of place or oversize for the neighborhood, and even though it is maybe equivalent to a $100 or $200,000 pricier house, people are not looking for ritzier houses than the surrounding ones, so it can actually detract from the saleability AND resale value. You always want to keep the property within the range of the neighborhood - people looking for a mansion look in Benerly Hills or Georgetown, not Canoga Park or in south DC, for instance.
There used to be a basic saying in the construction industry, back when contractors paid more attention to the client's well being and less to the $ - it was Build for How You Want To Live, Not For The Next Owner - with of course the proviso of not doing anything that makes the house odd or unusual, as that severely limits the potential field of buyers.
If you want a better feel for it after you read a few of the articles, if you have a friend who is a Realtor, or maybe the one you bought your house from, they are commonly happy (in anticipation of getting the future listing down the road when you move on, or that you will refer friends to them who are guying or selling) to do a quick walk-through and give their opinion on what type of upgrades will recoup a significant percentage of their cost, and which would detract.