So, the GM doesn't explicitly prompt for use of particular skills, though they might suggest an alternate skill to use if the stated skill isn't quite right? Or is it that you will explicity suggest a spend, but not the original use of the skill?
Do you have some principle or goal when deciding when to explicity ask for a skill, or to wait for them to suggest it? Or do you just wing it?
1) Yes. 2) Yes. 3) In my experience, players almost invariably ask for information without explicit reference to the ability. In response I ask them if they have the relevant ability. If they don't ask (except for plain sight information) they don't get the info. 4) Winging it: it's always better to go with what feels right to you at the moment, than to try and conform to an "official" way of doing it.
You really should post this article to the Gumshoe website, rather than charge people for it in the See Page XX compilation. With the release of Trail of Cthulhu, I imagine more people than ever will want to see it.