I'd paint the ceiling a spa light blue/green tone BM Ocean Air and hang shutters chest high when standing in the tub (no one is going to see you) . Or tile the ceiling with tiny mosaic tiles in a mother of pearl look.

The chandelier would not be permitted in my area for safety reasons.

Other updates: add heated towel racks and replace ottoman cushion.

I would box in, replace, or remove (if non-functional) the pillars. And remove the tub mirror before you paint. I like Lyn's Ocean Air for a paint color.

If you boxed in pillars, there would be no demo.

Consider removing the pillars and mirrors. In place of the pillars, add two small shelves on each side to have nice baskets for soaps, lotions, towels and a figurine. Paint walls and trim same as is being done in the main bath area. Shutters at the window covering 2/3 of size.

Artwork on each side that isn't loud, so the chandelier commands the space.

Paint ceiling, trim, walls the same dead flat sheen and same neutral color. Switch out chandelier for more updated fixture. What is out the window? Do you need privacy? If not ditch the blinds. If so, add half shutters.

I’d remove columns but you said zero demo. I think boxing them in could make for too many wonky angles.

As tub enclosures go it's a lovely space, well detailed. Likely fits with the design of the home.

The blinds look like a choice that doesn't fit the space.

I would have shirred patterned lace shears on rods instead.

Select an upscale stone for the floors

Select a coordinating wallpaper.

Agree with the flat paint and shutters - I’d also add a small fern or orchid on the edge to bring some texture and life to the area, think too about nice dispensers for bath products, little details like can make a big difference (Polished Jar is one site I like)

As most have said removing or boxing the the fluted columns will make a big difference. Also if those are mirrors in the alcove i would remove or cover them. These are not really big projects that even a “good“ handyman could accomplish.

I like the columns, they're funky. I'd get rid of the mirrors. If you did want to see yourself naked, they're probably fogged up.