I guess it's only natural that accordionists-who-compose will want to write music for their instrument. They can tailor their music to the tastes of their accordion loving/accordionist audiences or the style that's favoured for accordion competition music... However, to me there is something quite special when a composer decides to write for the accordion even though they aren't an accordionist. They seem freer and it's the breaking down of boundaries that separates the accordion from the other instruments - that makes me smile.
I would have loved it if renaissance, baroque or romantic music could have been composed for the fully developed concert accordion (free bass), but sadly we weren't around then. The periods of the great modal and tonal music passed us by. We've turned up to the party now and got served "contemporary" fare, that can at times be anything but tuneful - but the serious writers don't seem keen to give us lots of new accordion a la J.S. Bach.
It seems we are on a roller-coaster ride that's taking us on a crazy journey. I think many accordionists may feel like "a fish out of water" in this new world. All they wanted was a jaunty, toe-tappin' tune... sure, we can have that too, but it's now the preserve of folk and popular accordion styles.
I have to say, if I have the chance to listen to an accordionist playing F. Couperin or Ole Schmidt, I'll likely choose the former. However, in the interest of giving some ideas of classical (contemporary) music actually written for accordion it's the work of Berio, Schmidt and a few others that come to mind as interesting (to me).
Another current composer is Roberto Borin. I did not know of him, but it appears that some talented conservatoire students are being given the chance to play music that's been specially written for their instrument, straight out of the oven, freshly baked...
I rather like Wie auf einen Blick, ohne Schatten. It has something of the "light" about it.