@zante7,
I would not be concerned about resale if: 1) you plan on living in the house 5 years or more, 2) you are considering making the current bathtub space into a shower and sticking with standard dimensions so the next owner of the house can convert the space back to a tub if they so wish, or 3) have another tub in the house. Realize a few things: 1) if you replace the tub with a shower, the shower pan will need to be the same depth (back wall to front edge) as the current tub, 2) if you remove the tub and existing shower the entire floor will need to be replaced and the walls around the new shower will need to be finished with a non-porous surface (make sure you budget for this), 3) if you install a shower head over the existing bathtub you could capture the space occupied by the current shower for storage, etc making the room feel more spacious and you will have one less fixture to clean!

Keep them both separate for maximum appeal to buyers and resale value.

I actually think it's MORE functional to combine them. You could have some amazing storage instead of the shower, and everybody loves more storage!

Thank you for your helpful comments. If it was up to my husband we would live here forever but space is an issue or lack there of. I'm leaning towards keeping the tub but tiling it all the way to the ceiling and adding a shower head w a glass door. I would create a storage space where the old shower was. But here's another thought I was considering moving the toilet to where the shower is and creating a double vanity?? I would love to hear your thoughts on this