Add
- cool shower curtain (map, photo, really anything funky to jazz up the space)
- pain the vanity if you can't afford a new one,
- new mirror/ mirrors
- hang something on walls if there isn't tile there

GOOD LUCK !

The walls look yellow. Paint them white. Add some big fluffy white and aqua towels and a small framed picture with aquas. Pick a shower curtain with aqua and white.

I'd just paint the cabinets to match the tile color, and pure white on everything else. I think the tile layout in the tub surround adds interest- if you could do it at the sink that would be great. Are the tile colors the same?

All tile colors are the same but the floor also has gray. I like the idea of painting the cabinets and of course I would change the hardware. What about just changing the countertop. And would I paint the walls a gray tone? There is gray in the floor

What brickln said, except new brushed nickel or silver door hardware.

The countertop is fine. I suppose you could leave the cabinet white and go gray on the counter. Given the floor tile, your choices are kind of limited on the surfaces you could use. Not enough change to support the cost, IMO. Gray artwork or a touch of gray with the white linens would look ok.
Assuming the room isn't completely tiled, you could replace the sink backsplash with gray tiles and paint the vanity the same color, leaving the tub surround as the pop of color in the room.

I would do a classic blue and white bath. A bright new shower curtain like this one from Pottery Barn with just enough blue in it and new fresh white towels would make a big difference. If you have a little more money to spend and a little more time, I would replace the doors and drawer fronts on the vanity. We did that in this kitchen and it makes a huge difference in appearance of the cabinets. We ordered these doors and drawer fronts from Home Depot and when they came in we just had paint matched to them for the cabinet boxes. Then add new hardware and a new faucet. What are the measurements of your counter? White quartz would be beautiful. And, while I don't see any lighting fixtures in your pictures, switching them out can really update a room too. I agree with starr93 about having the floor professionally steam-cleaned and I love the bird print leelee suggested.