My definition of a hook is similar to yours but instead of a 'call to action' I would define it as 'cliff notes (or ideas) for the DM to start the adventure". This is my general way of designing an adventure.
Introduction: A little bit of story time. 1-2 paragraphs about the region, the plot--but no hard clues, etc. Sometimes this can be read/paraphrased to players if a 1 shot.
Summary/Background: A no nonsense spill of the beans description of what's going on in the adventure. No hidden surprises, just the total gist of what the dungeon/adventure is about, and the ending revealed. 1 paragraph is great...but sometimes more is needed if complicated. Sometimes....sometimes....this can lead to a hook, but it usually lacks flowery prose and color/spice. Summary/background is only for DM.
Hooks: Cliff notes for the DM to start the adventure. For planners (i.e. DMs running their own campaigns and reading the adventure first before play) hooks may not be as important, but for a DM just opening the book and running a game within a few minutes, it's a welcome mat and can be helpful to tie rumors/npcs together and give a path to starting the adventure. Hooks are another tool to incorporate faction situations as well as a mix of rumors. They bring in the spice and specifics and should never be read verbatim--rumors should lead to the hook.
Rumors: A critical piece to make an adventure feel alive. Clues for characters to explore or gather information about the region or situation--which can be true or false. Also a tool for the DM to guide characters to follow a hook if needed. And I will preach--rumors shouldn't just be in the tavern, but different rumor tables in different taverns, on the streets, from merchants, from other travelers, from other adventurers in a dungeon. "Make the whole world your quest giver"--YES! Totally agree. Also, a tool for guiding PCs to other parts of an adventure (back to city example, where rumors can guide them to different districts, where they will encounter a whole new bunch of rumors centered around that area, with a few leading them to even further districts/areas).
DM Notes: Anything that needs special attention.
I think overall DP, we agree that rumors are more important than hooks. But I still believe that hooks definitely have a place especially for a DM who lacks time.
A playtest is a one-shot by definition. So cut with the pretense and just talk to them as playtesters instead of trying to roleplay this stuff via hooks.
We playtest differently when its something large and just play it out as we would a campaign. Our 'one-shot' was over a year long and not everything was explored. Feedback is gathered every month or every other month and changes occur during play with written notes. Plus, we roleplay as part of the game, so having them roleplay is part of the playtest for us (it can also generate ideas for the DM to enhance areas or add new ones)---I understand that some have a different gaming style so your mileage will vary. I dont necessarily disagree as getting to the meat of the adventure (does the trap work as intended, this monster too tough, etc.) is important to eventually get too, but just describing how we do it.
Even new, shorter adventures, we usually throw into an existing campaign (if it makes sense) and run it normally as we do anything else. Our players (playtesters) usually don't know they are playtesting something until feedback is asked for. A high level adventure would be more of a one shot perhaps, but even then, our group would probably roleplay stuff out to get a feel for their character. Having said all that, I would say only 15-25% of the time is roleplay (and usually no funny voices (well sometimes if someone is playing 2 PCs) or costumes).
