Chris,
I have done some of the higher trails in Engadine and there were very few hikers on them. Some nice technical descents with singletrails that go on for ever without being full on downhill trails. One of my favorites is Val Suvretta near Celerina. The ride up is tough (you can get a gondela some of the way if you want), but there is a nice long singletrail waiting for you when you get to the top. Some great scenery, not so many hikers (don't go in august!) and fun trails. The only downside is that the altitude really does start to hit (2700m).

Check out the book, Schönste bike tours in der Schweiz for more ideas. Or most regions have a Mountainbike Erlebnis book. Check out the tours and use a decent map to alter the route to a more interesting one. I have discovered some cool routes by going a little bit off the published routes!