Many (better) hotels have explicit policies against wearing robes in the common areas. I've seen them enforced.
Regardless, unless I'm staying specifically at spa, count me among those who don't care to walk through those areas in a robe. Probably my upbringing, but always strikes me as tacky.
I always carry one or two lightweight, quick-drying loungers or sundress-type garments, which do triple-duty as a nighty and housedress (to wear in lieu of hotel robes, which are usually too huge and bulky for me to wear comfortably). They can be washed out quickly in the morning and are ready to go by nighttime.
And I never go anywhere without some kind of lightweight sandal or flipflop. Never. Even when living out of a carryon.
If you're not finding a garment that works for you, try looking in the sleepwear department, especially at less expensive stores like Target or Kohl's where they're more likely to have something in a lightweight synthetic fabric. You'd be surprised what's available these days to easily pass as a sundress. Added benefit of synthetic fabric is less likely to fade from chlorine.
ETA: Sarongs are great too. I use a very long, wide one that can be wrapped around my chest like a strapless dress.
~mrs