I like this idea, though I understand the reservations of many regulars. I'm still in that "no-man's land" you refer to, even after reading Sheldon's and Randy's sites a couple of times, and spending a lot of hours here. Yes, most newcomers people will post silly questions without reading that sticky or the connected references, but some might, and it would be an easy thing to point people towards. And there is a lot of garbage info out there, and dead links.

I'd suggest that sticky post be just an outline, with attached links, not an encyclopedia. For example, it might look something like this:

1. A bike that fits you is your first concern. As a quick guide, here is a height/bike size guide: [link] The 'size' usually means the seat tube length, but this is a tricky subject. Go to these sites to figure this stuff out [with links to Sheldon Brown key pages, fit guide, etc]
2. Don't compare apples to oranges. Understand that bikes are categorized by their best use. Figure out which type you're really interested in. Categories include 'touring,' 'racing,' 'townie,' .... Here are some links that describe the different types and subtypes ...
3. Most vintage bikes have frames made of steel of some sort. The quality of the steel tubing is a deep subject in C&V. In general, bikes with Renyolds 531 or Columbus SL tubing are likely to be nice frames. Here are some discussions...
3a. It is easy to add a sticker to a bike making it seem to have better steel, or a better model, than it really is. Here's a discussion of spotting fakes...
4. The collectibility and desirability of many older bikes is often based on their originality and appearance. Here are some links that discuss repainting, dealing with rust, restoration, etc...
4a. The desirability of many older bikes is often based on their functionality and rideability. Here are some links regarding using older bikes as daily drivers ... How to maintain them with original parts ... How to modernize them ...
5. There are some bike makers who are revered among collectors, and among some makers only certain models, from certain eras, are highly sought after. Names like Colnago, Masi, De Rosa, San Rensho are some top names, but there are many desirable bikes from lesser known makers, and sometimes a bike with a great maker's name on it isn't what you want. Some big name makers, like Schwinn and Bianchi, have made superbe bikes, and mass market junk ...
6. The components on a bike are a huge factor in the bike's value and utility, often outweighing the frame in importance. Often people buy a lesser bike with good original components to transfer to a better, more valuable frame that has worn out/damaged/missing original components. Certain components like Campagnolo Super Record are highly sought after ... Discussion links...
7. Pitfalls. When going to look at a vintage bike, look for the following common issues: stuck seat post, stuck stem, bends/dents/cracks in the frame, repainting that might be hiding frame damage, components that have been replaced with junk, rust in the frame, etc. Here's how to look for a bent fork: ... All these are likely huge red flags. Old/rusted steel rims are no big deal, though an extra expense to replace. Tires, tubes, bar tape, and cables will usually have to be replaced -- expect this expense and factor it in. If you buy a well restored vintage bike, realize the expense the seller went to...
8. At a minimum you will need the following items to deal with maintaining your vintage bike... Here's Sheldon Brown's discussion of maintenance...
9. Here are some classic parts of vintage road bikes that you should understand: [definition of lugs, dropouts, threadless forks, etc]

and so on. There are just a few of the areas that I've spent a lot of time learning about.

Also, for me reading the appraisals thread and 'are you looking for one of these ebay/CL thread' have really educated me about a lot. Also the 'show us your Raliegh/Tommasini/Centurion Ironman/Schwinn Paramount...." threads would be worth linking to.