Yes, you can use an older steel bike for rides like RAGBRAI, loaded touring or even as a road bike. I tour on a 1982 Trek 720 that I only recently upgraded to modern components. I once did a double century in less than 8 hours on the same bike, so there is nothing inherently wrong with using a touring bike for faster riding. A touring bike can be made to do it all, with the caveat that it will be heavier than a dedicated road bike and you will want a second set of wheels if you want to use it as a road bike. However, if you are only going to have one bike, it's a good place to start (at least until you are afflicted with n+1 disease).