Maybe the 1600 can list lines culled from a database, but as for "ideas" I doubt that very much. You should have a minimal ability to evaluate and organize ideas to write a decent book which a 2000 player would want to buy. This Mr. Hatch I referred to previously took care to write in his preface to write that his book on the Colle wasn't a "how to" book. Which is fine. But if a 1600 were to write a book called, say, Judment and Planning in Chess, I'd have a problem with that. Or How to Play the Queen's Gambit. I've seen 1600's at the club level read MCO and show a line they've seen. They show the line up to move ten and you say, "Back it up a little, what if black does this," and you plunk a piece down someplace they haven's considered." They go into a deep thought, but can't come up with a good answer, unless they run back to Fritz. I know ratings are often derided, but I think they represent, at bottom, a level of understanding. If a 16oo wrote a book for the elementary player, showing checkmates and basic problems, that would be ok. Along the same lines, when Andrew Martin writes a book on the Scandinavian (which he has), I as an 1800 am impressed and see things i could use. I'm sure if Kasparov read it he would say, "This line is stupid, this goes nowhere, etc. Ratings mean something.