synewave I think what you are doing is smart, and I don't see any particular downsides to it; but I have in mind people who have yet to complete RTK1, in that case my initial reaction is that there will be less focus on the writing and meaning, if there is more information to deal with.
As for finding interesting compounds, have you considered duplicating some of your entries? It wouldn't hurt to have one compound 2-3 times and you could then put the fill-in character in another position of the same compound. Just an idea. (That looks very much like the tests in "Nazotte Oboeru Otona no Kanji...." for the Nintendo DS in case you're looking for more compounds).
As for finding interesting compounds, have you considered duplicating some of your entries? It wouldn't hurt to have one compound 2-3 times and you could then put the fill-in character in another position of the same compound. Just an idea. (That looks very much like the tests in "Nazotte Oboeru Otona no Kanji...." for the Nintendo DS in case you're looking for more compounds).