Hey Steve. Here's a good forum to peruse for ideas. But don't let the name detract you. There are lots of good people and ideas there. Check out the pictures thread. You may need to register to see the pics tho.
Remove the tube, replace with shower surround (tile) and put a steam generator there. They can be picked up relatively cheap (around $800) these days. Likely, the property value will go up. Not too many homes that have a steam room...