I recently started playing the pure diatonic Jean-Ritchie-style dulcimer my wife built 50 years ago. No extra fret enhancements (6.5 or 1.5). For modal music, I love it's sound, ease-of-play, and slide-ability (something not possible on a chromatic). To expand its capabilities beyond noter-style playing, I've set it up with four-equidistant strings.
Exploring this instrument's capabilities, and developing proficiency and style in playing it, could last a lifetime. Musical genres that I like on this instrument are Appalachian, old hymns, traditional music of the Brittish Isles, Medieval, and Renaissance.
However, there are musical styles that sound good on the dulcimer but require more than hard-wired modal scales. For me, these are Jazz, Blues, Classical, Eastern European, and Klesmer.
Because I don't want to alter the beauty of my wife's pure-diatonic instrument by going down the slippery slope of adding extra frets whenever I encounter missing notes, I've ordered a chromatic dulcimer. But, for me, it won't replace my diatonic instrument for being able to capture the unique beauty of modal music.
updated by @lmcwilli: 02/07/23 04:21:56PM