If the Rockhopper is already built, I would already use it and sell the Marin. You are trying to make your life easier by selling the other bikes, and this is the path of less resistance. If, however, after a couple of weeks you are not 100% convinced on the Rockhopper, then yes, give the Marin a try.
If you try to use it as a tourer, fit and comfort should be first, regardless of components (and also, the less bikes you have, the more budget you can assign to the remaining ones). If the headset is ahead (likely in the ´97 bike) it will be harder to raise the bars, while the quill stems are much easier to move around. How many rack eyelets or mudguard eyelets might be another point. Or how many bottle cages you can mount. Which one has rigid forks... And so on... It seems you want this bike to be a do it all, so as long as both fit, get the more versatile frame.