I think spline is wonderful stuff. I used hardboard (masonite). You get over 40' of roadbed for under $10.00. It transitions so smoothly it's hard to tell where the ups and downs and rights and lefts actually start. I used 1" wide 1/4" thick  x  7 strips wide for mine.

I had a bit of a problem getting the tops even on the first couple of strips. To resolve the issue I clamped the entire strip firm to the next one making sure it was dead even at the top. I then would unclamp about two feet at one end and glue that with the glue gun. Once that was set I unclamped the rest of it and glued away. It went back against the next one the way it had been clamped. Make sure you put a screw through every foot or so. Drill a pilot hole first.

Using a rasp and a small level I put a bit of super elevation into a curve or two easily. Course sandpaper would do the same.

After having layouts built with all the methods I wanted to experiment a bit and try something new, so I used foam and spline on this one. So far I am delighted with the results. I have about 65' of spline on this layout. At $.15 a linear foot, the price sure beats the foam risers and unlike plywood there is little waste.

One more thing, when using spline you don't need a cork or foam roadbed as you caulk your track directly to the spline. If you are interested in seeing more go to Google images and search "spline roadbed".  It is another option.

Here you can see the beveled shoulder of the spline roadbed.

Here I am raising the foam up to the roadbed. I am doing this all over the layout. My hills are hollow.

You can use more than one method on the same layout. For scenery I have used foam, concrete, grout, thinset and plaster of Paris dipped sheets and towels. Think different products! It can solve a lot of problems.

http://www.youtube.com/watch?v=BXrYeMHw5j0&context=C3252b13ADOEgsToPDskLU1ohLLwpcdro7vyvEP1JQ

Good luck.