I'm currently developing a DSL. I definitely agree with what you're saying. Domain and technical expertise are needed in abundance. Writing a spec is HARD. It takes a certain perseverance to learn good parser design (I've written a great parser generator and I still feel inadequate in this area sometimes).

DSLs are costly. My concern is that the cost will outweigh the benefit and people won't like it and we'll be suck with it. My hope is that it'll stabilize and be expressive enough to fit everybody's needs.

Did you ever write a DSL used in a production environment? How complex was the DSL, more declarative or closer to a general purpose language?