How much better is a modern mountain bike than an "oldie"? Does full suspension and/or 29" wheels make a lot of difference on single track trail riding? I do push myself pretty hard but I don't race [or see how far I can jump ]. My terrain is mostly single track trails through typical New England woods - lots of hills (not mountains), rocks, and frequent water. I would do very little riding on pavement.
I went on a club "Mountain Bike Introduction" 25 mile ride last week. I was impressed that there were so many good trails locally and I was able to tire myself out a lot quicker than on my road bike. I'm riding 35-65 miles 4-5 times a week (3,900 miles since I started riding in June). It's getting cold and it seems like mountain biking might be a better choice soon (although I haven't dealt with ice yet).
I bought a MTB years ago and rode it quite a bit for one year. It's a 15 year old Nashbar 5000X hardtail with Specialized front forks and Umma Gumma (?) tires. [I am not sure about the year I think this link has info on the bike] It's in decent shapes (even the tires) except the forks leak down the air too quickly.
My guess is I will stick with my Nashbar bike (money is always an issue - I'm retired) but I like to learn the basics before I start on a major project.
PS - Any links (or advice or warnings) on how to repair the seals on the "Specialized Future Shock" front suspension (I haven't Googled it yet)?