Exercise is really important for them, I don't think you should remove the wheel. A trick that I has been working for me is to shut off the light at night at their normal time. In one hour I go in and flick on the light and they have pottied on their wheel but have not run yet. I quick wash off the wheel (we have the Saucer) and put it back and in the mornings it is about half as dirty as usual. Sometimes its even clean with just small specks that indicate it was used. I don't know what kind of wheel you are using but the saucers are much easier for me to clean than the large wheel I had previously. Link is for saucers at petsmart.
I wake mine around four p.m. at the earliest and play or cuddle with them all evening, their wheel activity doesn't seem to slow them down from interacting with us. Then we put them to bed and I do the "wait one hour then clean wheel" trick. I don't know what time they actually exercise on the wheel but they are able to handle both the wheel exercising and our interaction.
Instead of a full bath you can just put them in very shallow water with a towel to wash their little feet, less production. Or wipe their feet with a wet washcloth, I do that if its not excessive "boots".
If your little one is really slowing down, could he be warm enough? Do you have enough lighting all day? Now that its getting darker during the day I leave a light on all day up until I go to bed at night. HOpe this helps and I'm sure you will get more advice from others. I am still new.