those 4 people would be pretty cramped on the upward trip. You can do a rendevous faster but that takes quite a bit more propellant. Perhaps it'd make a better lifeboat or emergency vehicle rather than a routine taxi.

It seems possible to build a stretched version to use as a lifeboat, something along the lines of the Big Gemini proposal. You could launch it lightly loaded (say, with 2 people on board) and dock it with the ISS. It's possible that the Titan II might need a couple strap-on boosters to lift the extra load but that has already been incorporated into the design. Build it to be automated for the reentry and you're in business. It probably wouldn't have much crossrange capability but it'd still be a lot cheaper and faster to build than the CRV, and more flexible, too.