Here's my take on this problem. You already into a major job both for the amount of work and the expense involved. I would replace the old tub now while you have the demo on the room done. I have bone finish on my bathroom fixture, and that's working OK. However, if I was doing a complete remodel, I go to white. You could do that now, and I assure you no one would really notice. Actually, the worst part of replacing the tub is not removing the old, but getting the new one in place. You can take the old one out in pieces, but that doesn't work too well for getting the new one in. Perhaps your room layout is such that this won't be a problem.