How long have you lived in this home?
That's a great shower curtain and I bet it really helps. I doubt your kids care. I doubt that the company cares. And, honestly, I think the blue you have looks pretty good.
Here's the thing:
If you spend a bunch of money to reno your bathroom to whatever is in style right now, it will still be "horribly dated" in 10 years. Seriously. I just looked through pages and pages of early 2000's beige bathrooms (with the big square tiles) that people ripped out to put in grey and white big rectangular tiles . . . which will be "dated" by 2030.
I built a brand new home in the early 2000's with top of the line everything, 100% in style, fancy granite edge cuts and all. Looked like all the model homes in the parade of homes at the time. By 2010 all the realtors were saying "eww dated."
In my opinion, your bathroom will hold value better at this point if you embrace the retro nature of your bathroom tile and give it a few updates (like get rid of the wallpaper, obviously). The most recent posters had good ideas. I'm not sure what you should do about the toilet, because the non-matching seat makes it an eyesore. Sounds like the toilet and sink need to be replaced anyway, though, from what you wrote, and those things don't last forever. No one will blame you for replacing bathroom fixtures that are rusting out.
Lol, I moved and I now have two versions of your blue bathroom. Both have the similar floor tile to yours.
One is the pink bathroom.
The other is the brown bathroom.
Guess what? It's coming back in style. It's cool again. Seriously.
Our initial plan was to change both our bathrooms. Rip everything out and start over. But then we lived here awhile. Guess what? The "weird" square tub in the pink bathroom holds heat better than any tub I've ever had, and it's really big and comfortable. The tile grew on us. Instead, just like you we got new shower curtains. We decided to have groutmedic come out and clean everything and refresh and seal the grout. Wow, sparkles now! But, we did replace the rusted out wall mounted sink with a more modern white sink with a grey vanity in the pink bathroom. Toilet is also white. Put up a light grey shower curtain and small bath rug for getting out of the tub. Looks great! We are also eventually going to replace the brown bathroom's vanity, sink, and shower (The shower stall itself is a rusty nasty pit . . . you can't even imagine how bad it is.) But the wall and floor tile is staying . . . learn to love it!