It's a good idea, not in the least nutty, give it a go and report back.
Presumably they will not be in, so print off a few explanation notes to explain your actions.If you get caught say you are new and cleaning the wrong house.
The note should say something like- Please excuse the unusual approach(they all say that), and go onto to something like- on passing i happened to notice that your windows in particular out of the whole street were unusually minging-
When they realise the trouble you've taken to clean a couple of frames and see the difference they are sure to be thrilled.Make sure you leave a landline number as most people prefer this, and expect your phone to ring fairly soon.
Best of luck, keep coming up with the ideas.