I dunno if this will apply to dulcimer, but I get a wonderful sound on my autoharp with the lightest Jim Dunlop pick-- .013. Even with the pickup magnifying things, it sounds pretty clear. The downside is that they are so light they have some trouble staying on-- the wrap part is as light as the pick part so it wants to bend open. I use a dab of Mortite under the place where the wrap overlaps, to help it stick, and one of these days I'll break down and set up a few with filament tape. The nickel and the bronze (brass???) sound very different-- might want to try both.

Cheap experiment anyhow.

~Susan