Much as it pains me to admit it, as a retro mtb lover, modern suspension is much better than the stuff from the 90s. Nothing wrong with that stuff in its day but technology has improved.

If you like the non technical, single track riding then a hard tail is perfectly fine, even if you do a lot of climbing. I'm not sure about fitting a conventional suspension fork on to one of those Cannondales (perhaps you'd get better responses from the mtb forum) as they may have a 1.25" steerer. If it can be done I'd go for it as you are likely to see a big improvement in the comfort of the ride.

If you do go down the modern bike route then there are many good mid-range options around in the major names such as Giant, Trek, Marin, Specialized. As with road bikes, look around and try them out.