It depends - You need to find the manufacturer's directions. My example - I have a Dreamline shower base and surround I'm installing and it says that the base goes right up against the studs (no drywall behind it). It also says I do not need green-board or cement board behind the surround area , since its made of two large pieces of fiberglass/acrylic. However, this installation would be a lot different if I was planning to use tile, or was building my own shower base. Bruce

To all responders - many thanks for the comments and suggestions. Was able to open access door at plumbing end of tub and was able to see steel mesh and clumps of plaster below tub rim on exterior wall but no sign of studs - so I assume that plaster with mesh support is also behind wall tiles. This would explain erratic readings with stud finder. Exterior wall is brick - not sure if stud finder will give reliable readings through brick but will give it a try. If so will give me some general idea where studs might be.

Are you looking for something that adds function or for looks? A small table next to the tub would hold a drink. Do people actually read in the tub? I once tried but logistically it seemed more difficult than relaxing with a book in bed.

The overwhelming majority of demographics for your complex would prefer a great shower versus a mediocre tub/shower. Aging people who want to age in place need a shower - and as large as possible because stepping over a tub becomes increasingly problematic. Design with both function (bench and as many grab bars as possible to be reachable anywhere in the shower). While many older people are nimble up to a certain point, there are also periods when they might not be able to bathe and among my senior friends many have given up baths even if they previously enjoyed them because of difficulty of getting up from the tub. While you might lose a buyer who absolutely demands a tub in the master, the greater number will appreciate a great shower. And, if someone really wants a tub experience as critical, chances are they would prefer a larger soaking experience versus a tub/shower combo which doesn't provide the best experience for bathing or showering.