One place to look for ideas might be the Turkish saz - it's basically the same idea (fretted three-course instrument where the melody is mostly on the highest course) in a differently shaped package. There are many different tunings for the saz, one of the commonest is (for a two-course instrument) AA Dd GG (that is, the middle course is octaved).

There are far more saz players than dulcimer players and its repertoire and stylistic range are vast. Try Ali Ekber Cicek for starters - there are samples on YouTube, including his most famous song "Haydar Haydar".