A new vanity and fixtures can go along way to freshening up a bathroom. You would definitely want to paint, using the right type of paint for bathrooms (latex?). I would only replace the toilet if it is really old/damaged and uses more than 1.6 gallons in a flush. Otherwise, just reuse it and buy a new seat.
Do you have an exhaust fan? If not, see if you can get one installed - it will help save the paint job. Make your kids use it anytime they shower.
I agree that you can glaze or paint your wall tiles, though it is supposed to be a lot of work. I looked into it, and decided to pass on that. The results look good in pictures I've seen and I believe there are a few people in the area that specialize in this, if you live in the DMV.