Dropping $$$ on a mountain bike is really no different than anything else. A $20K car will get the job done, but generally speaking, it won't perform as well as a $60K car. Likewise for computers, TVs, etc, ad infinitum.
Frame design/material, suspension performance and lightweight (but robust) components are where the costs start adding up. The mid-to-upper end bikes have quite a bit of development and technology within them and, even as a hardcore hardtail fan who chooses my steel frame over my FS rig 9 times out of 10, I'm positive that most rides will be faster, more comfortable, and less fatiguing. I'm positive they'll be better in every category except the climbs, which given suspension design and lockouts they would close the gap a bit especially on rough climbs where the suspension can work in your favor for additional grip.
If your current Marlin is good for what you ride, then there's likely no justification for you to get a better (read more expensive) bike. That said, there are a number of bikes within the $3K range that are quite impressive (Devinci Django, Ibis Ripley AF, Norco, Kona, Knolly, etc all have reasonably priced but well built bikes). I'm sure the big names (Giant, Spec, Trek) do too but I'm not a big fan of the mega bike brands...
Frame design/material, suspension performance and lightweight (but robust) components are where the costs start adding up. The mid-to-upper end bikes have quite a bit of development and technology within them and, even as a hardcore hardtail fan who chooses my steel frame over my FS rig 9 times out of 10, I'm positive that most rides will be faster, more comfortable, and less fatiguing. I'm positive they'll be better in every category except the climbs, which given suspension design and lockouts they would close the gap a bit especially on rough climbs where the suspension can work in your favor for additional grip.
If your current Marlin is good for what you ride, then there's likely no justification for you to get a better (read more expensive) bike. That said, there are a number of bikes within the $3K range that are quite impressive (Devinci Django, Ibis Ripley AF, Norco, Kona, Knolly, etc all have reasonably priced but well built bikes). I'm sure the big names (Giant, Spec, Trek) do too but I'm not a big fan of the mega bike brands...