Were you planning to expant the room itself, or move things around in it to flow better? It would be helpful if you posted a few photos, and even a sketch of the layout, so we could see what your options are.

Can bath be expanded by stealing space from an adjoining room (does any wall back up to a closet, for example?).

To make a small bath appear larger: get a floating vanity that doesn't touch the floor (more floor showing equals more spacious). Use large neutral tile on the floor and something similar on the walls. Can window be enlarged for more outside view?

are you planning to renovation other parts of the house ?

Are you planning on replacing the galvanized supply lines and/or the cast iron drain lines?