Andrew; lots of other and more consistent producers in Nahe, so I wouldn't worry about Diel unless there's a sudden closeout. I've seen Marty's and a couple of other places clear Diel out every now and then (shocked and appalled, again, that those wines wouldn't sell at those prices!
) so keep an eye out.
But I think that Kruger-Rumpf and Schneider usually offer the same quality for the most part - occasionally Diel's sweeter wines from Goldloch and Pittermannchen can be truly outstanding, but K-R's Dautenpflanzer and Schneider's Hermannshohle Spatlesen in recent years have been on the same level.
And of course Donnhoff and Schafer-Frohlich (and often Schonleber) are playing in a different league to Diel, with much more reasonable prices. When there's Bockenauer Felseneck or Norheimer Kirschheck/Felsenturmchen Spatlese to be found under $40, I'm not bothering with any of the Diel wines.