The tub/shower combo in the guest bath and the soaker in the master will be just fine, I think, especially if the secondary full bath is located near where under other circumstances the children's rooms would be. Just make sure the tub to go under the shower is a nice one, not one of those glorified shower receptors that doesn't hold enough water to bathe anyone over four years old. Vertical grab bars positioned on each end wall near the edge of the tub can help people get in and out of a deeper tub for showering, although those with real difficulty could use the 3/4 bath (two guest baths, must be quite the place). I am one of those "confirmed bath people" and if the guest bath only had a shower I would be quite shamelessly asking to use the tub in the master! Pharaoh, it's interesting that you say tub/shower combos are "apartment like" - this is the first house I have ever lived in that had a separate shower and tub even before we put ours in, although there's a tub/shower upstairs. Our rented house had 2 3/4 baths and both full baths had a shower/tub combo (acrylic one-piece modules, in fact, and these weren't inexpensive houses), and virtually every house I lived in as a kid - I moved around a lot due to my parents' divorce - had them. (A couple of the old houses didn't have showers at all, just a bathtub with a handshower attached to the faucet.) I don't know anyone else IRL who lives in a house that has a separate shower and tub, and when we were househunting we looked at dozens of houses and none of them did either. The house we are buying has only one full bath and it has a shower/tub combo; while a separate shower and tub would be very nice to have, it would take major construction, basically reconfiguring the entire second floor, to make enough room for that. I wonder if you just see way fancier houses than I do, because to me the tub/shower combo is the norm and a separate tub and shower is the "super size it".

I was going to suggest the same as juliekcmo. Rip out the tub, cap off unused plumbing so a tub can easily be put back in. Don't get one of those big solid shower units, use tile and keep plenty of extra (and grout!) 'just in case'. You're going to have to think about a shower door... that's actually a bigger decision. Do you want to spend the money on a nice frameless one (would appeal to buyer that doesn't mind not having a tub) or do you just use a curtain? (would appeal to someone that's going to put in a tub-less tile to repair). Ripping out the bottom of the shower and plopping down a tub won't be a deal breaker if a prospective buyer loves the house in every other way. I wouldn't offer an allowance right away unless they asked for it or I would use it in a counter offer. Your realtor will give you feedback-it might be necessary to offer it right off the bat.

Ah the great debate. I just ripped out the mediocre tub/shower combo in my master so I could have a great walk in shower. My other bathroom only has a stall shower. Since I never take a bath, why should I deprive myself of what works for me because some mythical homebuyer down the road wants a tub. Most adults prefer great showers to mediocre tubs and many people who have the room for separate tubs post that they never use the tubs anyway. People say that you need a tub to appeal to families with children. Children don't need to be bathed in a tub for that long and can be bathed in a big plastic tub in a shower if need be. You would probably have just as many buyers attracted to a great shower anyway who wouldn't miss the bath.

If one of the two baths is an en suite devoted to one bedroom, I would say it's worth adding at least a half bath. If you have the space, go for a full bath. An extra toilet is nice and even just a small standing shower can help make your home run more smoothly when all of the bedrooms are full. I don't know the exact trade-off on resale. There are a lot of factors that will determine that, including the finishes you choose in the bathroom, the cost of the work in your area, and the overall impact the bathroom has on how your home flows and fits together. A bad reno can be worse than just leaving the house as is, so the question of "will it help resale?" can be really tough to answer without managing the project every step of the way. Example: Removing the master bedroom's walk in closet to add a bathroom or adding a bathroom that opens directly into your once fabulous kitchen.... Probably won't have the desired trade-off. Those are some decently obvious pitfalls, but there are many, many other less obvious ones that would only come up on a case-by-case basis. That said, I've been doing a lot of research on bedroom:bathroom ratio. It isn't an exact science, and I didn't crunch hard data, but anecdotally, this is the estimate I come up with. If n is the number of bedrooms.... The number of toilets should be at least n-2. ... 4-2 = a 4 bedroom home should have at least 2 toilets. The number of toilets in the home gains little above n+1. ... 4+1 = a 4 bedroom home gains little value from having more than 5 toilets. So, having between 2 and 5 toilets is good for a 4 bedroom home. The home loses sell-ability with only 1 bathroom. The resale increase diminishes for more than 5. The number of showers in the home should be at least n-2. ... 4-2 = a 4 bedroom home should have at least 2 showers. The number of showers in the home gains little above n. ... 4 = a 4 bedroom home gains little value from having more than 4 showers. So, having between 2 and 4 showers is good for a 4 bedroom home. All homes should have at least one bathtub. If there is only one bathtub in a home that has at least 3 bedrooms, that bathtub should be kid friendly (most people buying 3+ bedroom homes are parents or people planning to be parents). I haven't figured out a rule of thumb for when it becomes necessary for there to be a second bathtub, but at some point, more bathtubs become essential to provide the luxury that fits the home. Hope this helps.