I superelevate the curves on my mainlines. I handlay, but you should be able to adopt the idea to flextrack. Prior to glueing down the ties, but after drawing in the centerlines, I glue ties end to end along the length of the outside edge of the curve, starting about one foot before the start of the curve. I then sand down the ties for a distance of about a foot so as to provide a "ramp". Then it is a simple matter to lay down the ties, ballast and lay the rail. For flex track, I would think you can do the same, the wood ties are a good thickness, I have no idea how they relate to the prototype height. They are easy to install and sand. The elevation is noticable, and trains look great going thru it. I don't think it adds anything to the performance. If you wnat to run at high speeds around fairly sharp curves, the amount of superelevation you require would likely be much greater than a tie. And then slow moving trains might have a problem. It might look unrealistic. Hope this helps.
Gary
