It's not that hard to find narrower vanities (19-20") and that might help. I agree with weedyacres, maybe consider a pocket door for the bathroom door.... 31" clear for the toilet is just barely enough IMHO, next to a vanity. A couple more inches would feel much better. As far as tub or shower... how do you envision using it? For example, would it be the place to wash dogs or really dirty kids or soak houseplants? In that case, a tub might be more useful. if it's just an overflow, occasional use shower (or for resale), then a small shower would be fine. I am not sure it'd be necessary to go with what most people consider the minimum comfy shower size (3 x 4) if you'll rarely use it and you're trying to maximize the space... I guess what I am saying is: what are the priorities for this space?

Yes, unless there are other compelling reasons to remodel, I'd consider that kids grow up pretty fast and leave it alone, unless you have constant guests who must have their own bath whom you consider worth that kind of outlay. But roarah is right: if you want something bigger than the room you have, the space will have to come from somewhere, unless you're a tardis engineer. :)

For those who like the immersion of a tub and the moving water or massage-like functions, but hate the gunk and the noise, one company makes jetted tubs differently and those issues are supposed to be minimized or eliminated. They used to be called Sanijet and Spike had a policy against allowing us to even mention the name because they had violated his strict anti-advertising policy. I got a warning just for asking about them. (For you Houzzers who never visited us when we were THS, it was strictly forbidden for even the Pros who contributed to the discussions to even mention their company names before Houzz bought the Garden Web and This Home Site) Now, the company is named Purewater Baths. Pipeless Technology at Purewater Baths Each jet is a separate electric motor and there are no pipes under the tub going from jet to jet. So no microbe-filled gunk will greet you when you start jets that have been sitting unused with stagnant water sitting in the pipes since the last bath. Since there is no central pump, there is no vibrating motor making noise and humming for all the adjoining rooms to hear. It is supposed to be a technology that allows you to talk, listen to music, or watch TV, if that is what you want to do while soaking. Also, when installing a conventional jetted tub with pipes, you should be able to elevate the center of each plastic tubing pipe so that it always drains clear after using the tub. This would help with the dirty water/gunk issue. I always wanted to try one, and had hoped for years to someday have one, before arthritis and my other joint disorder made getting in and out of tubs impossible for me. They are more expensive, but I was willing to save for that if it made the bathing experience worthwhile. For those voicing objections to the gunk and the noise, I thought that letting you know about this option would be beneficial.

A picture? Is it one piece or is tub and walls separate?