Personally, if given a choice between the Specialized frameset and the BLT frameset (ignoring cost and resale value) I'd choose the Specialized. So for me it's easy: update the Specialized to suit my needs and then ride it. Yes, there's renewed interest in classic tourers, but as pointed out, the Specialized isn't exactly Fausto Coppi's 1949 Tour de France bike. It's unlikely that anyone's buying Specialized Expeditions to hang on the wall. It's going to be ridden one way or the other, so it may as well be ridden by you!

Beyond that, it's not as though you're planning on cutting off the derailleur tab and rattle-canning it. Even if you did someday decide it should be "restored", just unbox the stuff you removed and reinstall it.