Consider having the tub surround tiled to the ceiling, and paint the entire room a soft complimentary color. It's a nice size space!

I would definitely paint, change the mirror to two framed mirrors if there is enough space, get a new light fixture and upgrade the towels 🙂

Bring in another color with a new shower curtain, a rug, and a apinting or photograph on the big wall.

Great shower curtain hung high
Frame out vanity mirror
Tile over that stripe

Paint - no more stripe. High shower curtain, frame the mirror, new light.

Voting for a simple paint over of the strip, then the world opens up ! You chose well with the all white room as a simple change of shower curtain can be the basis for a whole new scheme with towels, dispensers and even quality faux plants if you are not blessed with a green thumb. Some curtain ideas to launch from…..

Paint, no stripe, use a very light color. The bathroom looks great, dont change anything else.

Lots of good ideas already. One that wasn't mentioned was to change or even upgrade the flooring. The current floor is too similar but doesn't match or coordinate with the adjoining floor. Maybe a faux stone look LVP for now. Eventually a higher cost upgrade would include a tile floor and alcoved shower.

Next, I agree with removing the stripe and getting longer shower curtains you can hang higher.

If you still have funds, consider framing the existing mirror or replace it with framed mirrors.

new vanity, mirror and light fixture. Paint or paper. Keep shower curtain closed if not enough money for tile around the tub

I think it looks fresh right now why not change the stripe to a new color add some nice colored towels and maube anew shower curtain with a color that you use for the stripe and please do not close the shower curtain IMO if it closed it looks like you are hiding a dirty shower and tub. I like simple clan bathrooms and you have that You could if oyou really wanted to add some art on the wall maybe a new light. BTW if you ever want to do a real redo get a nice soaker tub.. When painting those new stripes get hooks for the towels no one ever folds and hangs towels nicely

Great bathroom! I would put the money into getting a glass shower door and paint.

Add some color--paint, rug, shower curtain, towels.

Change out the faucets and perhaps replace the large mirror with 2 smaller ones with frames.

Those sinks look huge and eat up valuable counter space. Are you washing twin infants at the same time?🙂 Who uses that space, and what is his/her opinion?

Like others have said, the biggest bang for the buck is a pretty shower curtain and paint.

A new light fixture is a must, but if you are doing the work yourself this is still just a couple of hundred dollars.

Replacing the tub and doing a tile surround will break your budget.

Where I would spend money is the vanity area.

I would replace the vanity with a single offset sink with one side having drawers and the other having the sink with a cupboard base. Offset sinks are a bit more difficult to find, but with a 48" single sink vanity that is centered you will need to have plumbing moved and you get 2 sets of 12" drawers that don't hold anything.

When I did my bathroom I needed 18" drawers on one side and 12" on the other and ended up buying base cabinets from Home Depot rather than a prefabricated vanity and then had a counter fabricated and installed. This option was the least expensive route, but the counter fabricator had a minimum charge that would have broken my budget for the one bathroom, but I had two bathroom counters done at the same time that added up to just over their minimum charge. It took research to get exactly what I wanted at the price I wanted.

Picture during reno. With my electric toothbrush, water pick , tray with perfumes . . . on the left it doesn't feel off balance and provided me with the best storage and I didn't need to move the plumbing. (Original vanity was a 48 and had 7" gap between the vanity and the wall.)

To my surprise I also found that getting my mirrors from a local glass cutting place was much less expensive than buying prefabricated mirrors. They came out, measured the space, cut the mirror including the whole for the outlet and installed for just a few hundred dollars. Again this was done for both bathrooms. One 57" mirror and one that is 8'.

Great suggestions already - agree with a new shower curtain, I would hang the rod high and get a custom length curtain that just hits just above the floor (we got ours off Etsy) and I would also add a terrific Ruggable with some pattern and more color - it will be more refined details that bring the bath up a notch

Same as all the other economic ideas:
Shower curtain
New paint
Nice rug
Coordinating towels

A little more money:
Wallpaper
New shower curtain
Nice rug
Updated faucets

Whatever you do, artwork can brighten a bathroom immediately.

Reconsider your flooring. It really clashes with the hallway floor, which I’m assuming is throughout that entire level of your house.