Your needs and personal preference should always prevail. However, one should never lose sight of the distant possibility of selling in the future.
With this said, it's not the size of the bath that is a major concern but the fact that each level would have greater appeal with both toilet and shower/bath accomodations. In our opinion to remodel and eliminate totally the shower/bath arrangement could be a great mistake. Each bath should have either a shower or a bath for best resale potential.
Good luck with your project!
If you are not planning on selling than I would make the improvements to fit your lifestyle though it sounds as if your downstairs bath is so oversized that you may even be able to reduce the size greatly without losing the shower. For resale that would be my recommendation. Having the second shower will certainly open you up to a larger market of buyers compared to just 1 bath and a half.
Your Savvy Realtor