gmtfd - I remember the experience you are talking of. The authentic experience of the 90's was essentially extreme terror on steep downhills, an inability to jump over anything, and a lot more fear of everything - not least because early brakes were terrible. You can replicate all this by removing the brakes from your new bikes, pumping up your tyres to 40 lbs, leaning right over your bars, and screaming.
You can make a retro bike perform really well by - making sure you get a largish frame - the Marin RR sounds good. Use an inline post to get a steeper seat angle. Use a shorter stem than usual, and use old riser bars. Get the widest retro rims - like Mavic CDs - and use wider tyres. Use V brakes or really good cantilevers like Critical Racing with decent levers - XT for example. All this COULD have been done in the 90's. And some of use WERE doing this - Team Marins with LOOONG tip tubes, inline posts, short stems, riser bars, top cants. Reduced the fear factor. Increased the pleasure.
Subjective, used to jump with no problem, brakes are fine if you know how to set them up, and some of my retro bikes preform better than my modern bikes on certain trails.