I've been thinking more about Wilderness as Dungeon. One of the core elements of old-school dungeoncrawling is attrition-based, resource-management-focused gameplay. In the dungeon, this works well, because at the timescales under consideration, HP and spells are not restorable, so a series of easy encounters can grind you down if you do not manage your resources carefully, with random encounters serving to discourage playing too cautiously.
This is not the case in the wilderness, where a journey is measured in days and consequently spells slots and HP can be restored by camping. At the movement rates we typically see (fighters in plate on foot with 60' movement translates to 12 miles a day, usually reduced further by rough terrain), you're only looking at one or two random encounter rolls per day, and less than one encounter per day in expectation. About half of those can be avoided by a good reaction roll. So you'll probably only have a fight every couple of days, which means the party will be well-rested, with full HP and spell slots in most combats. This is a state of affairs which nominally agrees with them, but actually has dire consequences.
This situation is very similar to that produced by the Five-Minute Adventuring Day in 3.x. Fights have to be really, really dangerous in order to matter to the resource-management game at all, and the unit of resources managed becomes corpses and consumable magic items rather than HP and spells. I'm not sure this is desireable. The sheer size of many wilderness random encounters suggests that the
game's designers might have been aware of this, and chose to escalate, but I don't have enough data on the earliest days of wilderness adventuring to conclude that definitively.
There's also a feedback loop here - the more cautious the party, the deadlier you have to make combat encounters to matter, and the more cautious the party gets. Psychologically deescalating back down to slow-burn attrition is very difficult.
If you could only restore spells by resting and reading in a comfortable, indoor environment (can't have stray winds blowing your ritual foci around, you know - mucks up the feng shui), or praying at a properly-sanctified altar, establishing a domain out in the borderlands/wilderness near your main treasure sources would become a lot more imperative. Accompanied by a decrease in wilderness encounter difficulty from existential threat down to chip damage (not lairs, though - those should stay dangerous), I think this would extend the dungeon attrition model out into the wilderness effectively. An alternative would be to reduce the rate of spell recovery in the wilderness rather than eliminating it entirely. What if it took a whole day to recover spells in the wilderness? What if it took an hour per spell level, and you had to start with your lowest-level slots expended? What if recovering spells in the wilderness were dangerous, exposing your mortal soul/astral self to the hungry Green Chaos and risking corruption?
Two other alternatives present themselves. A party under time pressure cannot afford to crawl along at 12 miles a day, and moving faster increases their risk. It is also possible that at higher levels, wilderness encounters become much less threatening, and players will of their own volition choose to move more quickly because they have the resources to endure multiple encounters as they currently exist. This might be similar to how 1st-2nd level dungeoneering plays - any encounter is potentially deadly, so the party takes great caution, but at higher levels the dungeoneering dynamic changes somewhat, then resets to high lethality at 4th-5th in the wilderness, which then tapers off again.