Well, looking at the amount of work involved (and cost) we've decided that we're probably not going to replace the whole shower in our guest bedroom after all (I posted earlier about opaquing glass).
The tiles are yucky but I guess a bit of tile paint will deal with that. What's a bigger concern (and more offensive to the eye) is the shower tray which is early 70s faded mustard colour and seems to be made of tupperware. (Slightly bendy and supported round the edges with a metal frame, not foam filled) Just changing the tray would probably be a lot more work that changing the whole damn shower what with drain access problems and so on. I don't suppose there are any paint products designed for surfaces like that are there?
The room only gets about 2-3 weeks use a year so it's hard to justify ripping the whole thing out and whatever we paint it with isn't going to suffer a lot of wear and tear.
Tim