This track (or these tracks rather) will be even tricker to work with due to their proximities and the way some of the elements were design. Smoothing will be quite a chore and building good terrain will be even harder. You'd do best to use a custom terrain texture that contains the areas with dirt colored in accordingly, or better yet, use 3D objects to simulate different terrain surfaces. Of course, it wouldn't hurt to add 3D objects of pathways, etc.
Three Monkeys is a classic. I'd say, take your time with this and get it as good as you can.
I'm actually working on a classic RCT ride myself as a side project, though the trackwork is completely unacceptable at this point but even when I manage to get it working nicely, I'll be spending time on custom textures, trees, environments, and 3D objects for the rest of the park. I won't reveal which park I'm working on until I actually get some progress done on it.
On a side note, I'd suggest adjusting your graphics settings in NL accordingly. At least set everything to 32-bit color so the mountains don't look all messed up (and 32-bit color shouldn't hit your framerates at all unless your computer is running Windows 98 or something); the rest of the settings should be done based on how powerful your graphics card is.