Things have slowed down here a bit so I'll have a stab. Thanks for the thread and the excellent input everyone. I've done a little exploring, a little thinking - I may have set the smoke alarms off with all the effort - my brain hurts - I'm not, by any means, an expert on the subject.
It's Interesting that the mineral oil referred to in Poncherello's link
↑, is used in
↑ as
a LAXATIVE! Wouldn't
that give you the sh!ts. Coincidence? I think not. I do think good 'lemon' oil is pretty much the same stuff, with a little added 'smellnice,' but perhaps not food grade smellnice. I wouldn't use it as a laxative, just to be sure
You can see the ins and outs of it described
here, in a
"JOINT FAO/WHO EXPERT COMMITTEE ON FOOD ADDITIVES" report from 2012, where it's listed as a food additive. It's actually used as a lubricant for moving parts in food prep machines and the like, if I'm not mistaken. Good to know it's not harmful ' though the fine print is 'interesting.' (Boring, boring! I know). Meanwhile…
Mineral oil's most salient feature, at least where its use on raw wooden surfaces is concerned, is that it is pretty much inert. Most pointedly, it's not gonna rot. This is particularly good news for people who like to put wooden instruments in their mouths, and don't they know it!
Organic acids, which are often a naturally occurring, stench-laden byproduct of decay - a mishmash of rotting organic matter, like branches, leaves, and other plant and animal matter - are a genuine, corrosive threat to just about anything. One organic acid, humic acid, for example, can, over time and with a little help from the heavens, drill holes through solid rock.
Huge holes.
Water, rotting organic matter, and humic acid, created a natural pool here - now it's a waterfall called the
Link Removed.
If this kind of chemical process is going on, even on a very small scale, on a fingerboard,
or anywhere else, there will no doubt be trouble, over time. Maybe this is the real benefit with something like mineral oil. It can virtually shut down the natural processes of decay, in many ways, cleaning away and nullifying all the gremlins and other dirty rotten nasties in the process.
When I asked my luthier friend, a great man, how I should clean his heavy metal masterpiece, he just handed me a bottle of lemon oil - bless 'im. Little else was said. The subject was 'cleaning.' He said I could treat the whole thing with it too - I was mainly concerned with the fretboard but still, I had to ask - it's a Les Paul copy with a lovely nitro finish. I had no idea, back then, no confidence what-so-ever - and I'm
still learning. (OP's thread's going along swimmingly
.
Everything's subjective but that's cool.)
I think he told me not to do it too often, and not to use too much. I promptly forgot this and probably oiled the thing a little too often for the first little while. Too much love is not a good thing, sometimes - still, no ill effects. And I've wised up just a tad since then.
I imagine, if you don't use too much oil, you might be able to do it more often but, always, the question to ask yourself is 'Why?' One rule of thumb is to always keep the digits tickety-boo, wipe down habitually, and oil only when it seriously looks like it's time to do it. Noted - that people in colder climbs have seasonal justification, especially before the onset of winter. No such thing as winter here. Not a problem.
Things are going along swimmingly with the Les Paul (and the Superjazz and the PJ - I'm pretty big on rosewood, just quietly - starting to think this may not be such a good idea

) - it's a thirty something year old guitar now, that I've had for over twenty years. The neck has not budged,
EVER. So, it all seems pretty cut and dried to me - remember I'm only doing what I was told - if you don't go overboard, and you do it right, more or less, It really doesn't hurt to do it. In fact, I
think it does exactly what it's meant to do. No worries.
Lastly, regarding environmental moisture levels and humidity: I don't think any treatment's going to turn back that tide entirely. I've learnt that ambient humidity is going to complete the equation in a wooden instrument's formulation, no matter what, so the best way to accommodate
that reality is to make the instrument in the very same environment where it will be living. I say this because I was once asked where
I would be living. Interesting question, no? Struck me that way.
I lived on the East coast and had no plans for a change of scenery. Apparently though, if I was going to live inland, away from the coast, in a radically different environment, the woods used in my guitar would've been treated very differently, before the build.
Could it be that, if I was to be a desert dweller, the Maestro was going to synthesize a desert climate? In hindsight, I believe so. Whatever the case, for my money, he chose wisely. I now have all the evidence
I need. (Still, no clue, really

These people, who make these instruments, are unfathomable freaks - always passionate and perpetually inquisitive.) Thanks again everyone, for all the insights.
[Edit] NB: If you have any crazing on a finish, or any other damage where the surface of the wood may be exposed, best not to use lemon oil on that. The oil will probably get in under the varnish and things could get a little ugly.