As you've already said, keep your favourite(s) as once you part with them you'll probably never be able to own them again. Owning something as way cool as a Yo Eddy would be great, but the modern bikes ride so much better.
I still race my '96 Dyna-Tech Torus FS (though many of the components originally fitted have since been replaced for functional reasons) but if I broke it trail riding a) I'd be heartbroken and b) I'd never be able to replace it. So I bought a Giant Anthem. Having also rented a hardtail 29er in Italy and ridden some proper bouldery natural, ungroomed trails, I have to say they are so much easier to point and go over pretty much anything. You can drop, lean, grip and grin at high speeds and generally have lots of fun. My opinion is these bikes are easier to ride than a 26" wheeled retro machine, so you can take on even more challenging terrain. Take the plunge if you haven't already...!