Howling Emptiness of the 5/6/8-mile Hex

(yes, the titular reference to Rob Conley's mapping bugbear is intentional)

This is just a half-formed thought inspired by noisms and steamtunnel's recent posts on just how big and potentially full of adventure even a single 5/6/8-mile hex is.

Hex map icons, by their nature, only indicate the single most salient feature to be found in that particular 21/31/55 square miles of landscape. Sure, you can drill down to a more granular level with the help of nested hex map templates (such as Welsh Piper's fine 1/5/25-milers), but creating a whole new map for a smaller-scale area is a whole extra chore for the already-busy GM. I don't know about you, but I want to minimize my level of extra work thanks.

Could we perhaps add a simple 'emergent exploring' rule that allows the party to uncover more stuff (up to the limits of the GM's taste/patience) the longer they stay in a hex?

• Castles, cities and the like should all be in plain sight unless intentionally hidden away (like Gondolin or Derinkuyu). Heck, roads point you directly to most of them.
• Infamous lairs, ruins and dungeons should, of course, retain their "Here be dragons" hex map icons and easy-to-find status. The yokels can point out exactly in which direction the castle we don't go near lies.
• More obscure lairs, lost ruins, buried tombs and especially treasure map loot should require a bit of active hunting out by adventuring parties.

I was thinking either some form of skill check per day of exploring a hex (something for that otherwise worthless Halfling to be doing with his time?) ~or~ an standard Xin6 chance per day of uncovering a particular feature. In either case the base chance can be modified up or down for degree of obscurity, concealment, speculative vs. purposeful searching, etc.

Perhaps integrate this into the Wandering Monster encounter rolls that are already part-and-parcel of wilderness exploration in Classic D&D? Just tack the 'discovery' chance onto the existing roll so that it goes from being

d6 1-2: encounter, 3-6: no encounter

to something like

d6: 1-2 encounter, 3-4 fruitless wandering, 5-6 Eureka!

with the Eureka! result representing discovery of a previously known (to the party) but locationally undetermined feature.

"I told you the Tomb of Screaming Death was out here. Pay up."
"Alright, but I want a discount for the sheer length of time you dragged us around this filthy swamp."

Thoughts? Suggestions? Accusations of reinventing the wheel?
Is there already such a rule hidden away in the TARDIS of a game that is OD&D?