I think it would enhance resale to have at least a shower.

If you are going to live there for twenty years I wouldn't worry too much about it because maybe it will be time then for the next owner to redo the bathroom, but you may want to make the layout amenable to converting a closet back into a tub or shower area.

I've wondered the same thing about the full bath on my main floor, but decided to leave it as is. I won't gain anything by removing the alcove tub/shower, other than a bit more space in the room, but I will lose my prime dog washing spot ;)

You didn't mention how many bedrooms, so if you have a 2 bedroom house, 4 baths would just simply be wrong.

Let's look at it from the buyer's perspective so let's say you are the one looking to buy a house.

In this imaginary scenario, if you wanted to buy a 4 bedroom house, the difference between a 4 bedroom 1 1/2 bath house vs. a 4 bedroom 2 bath house likely appeal to you (and certainly to more prospective home buyers). You would see a higher selling price in most cases too so let's switch gears and now make you the seller.

You could apply some changes in the "redo" to play down the bath part and have the "powder room" become the main highlight. However, in real estate, more can be more and if the "bath" looks like an after-thought, it could negatively drive down the selling price, so careful consideration should be used when contemplating the new design.

So, since selling is about having interested buyers, think of the many listing services and real estate search engines today that will not show a buyer who searches for a 4/4 home any of the 4/1, 4/2, 4/3, or 4/3.5 homes - that means you aren't appearing in as many listing searches. However, listings for a smaller 4/2 would also show the 4/2.5, 4/3, 4/3.5, etc... - basically a listing shown to more prospective buyers.

Another example is that it is all too common that many home owners believe they will stay in their home for decades but often don't due to some unforeseen disaster, health issue, relocation, tired of the old house, neighborhood goes down, a foul smelling or noisy business goes in up the street, etc. I know a couple, who planned to retire in their home, only to move within two years of purchase because their daughter needed help with her very sick baby.

Making a room into something to be remodeled later doesn't really work because fewer buyers want to buy a "gut and remodel" home which is definitely not a selling point by highlighting what something "could be".

Any issues in retirement could also limit your funds to properly remodel yet again for the purpose of selling plus remodeling will likely be more costly in the future than today.

So what's the bottom line?

Living in your home - you need to be happy, so do what makes you happy and don't worry about the what if's; but should having a main floor bath make you unhappy, don't do it. If your home is two bedrooms, don't do that either. For any other reason, if you don't mind the extra bath, it certainly can't hurt and will likely help should you ever decide to sell.

Who knows, when your retired in-laws need to move in with you, having that extra bath may help out tremendously.

Even if you don't have any bedrooms on the main floor, if you/someone in your family breaks a leg/trashes a knee, they will not be going upstairs for a week or more. Unless you have a full bathroom (ideally with a shower, not a tub), how will that person take a shower?

You don't need to be elderly to need an accessible bathroom.

I'm adding a shower to the powder room on my main floor. All the bedrooms are upstairs.

There have been several times when I have really wanted a shower on the main floor - recovering from injury or surgery, elderly parent 2-week visit and not able to manage the stairs, or just my kid coming home with sandy feet from beach camp.