Thanks for taking my reply in a constructive way, it was late when I wrote it and it’s more full of "no"s than I’d like in the stinging light of day.
The tricky thing is the problems seem to be a bit at odds with each other, on one hand downtime is too grindy, on the other hand if fast learner works as intended (converts xp into skills faster), your jaunts to spend XP on things will be even shorter!
After some thought the benefit of fast learner (as intended) is to reduce the non xp cost of raising skills. For crafting it’s mostly materials and time, for combat it’s exposure to danger (and somewhat resource expenditure and time). To keep it focused and balanced, I wonder if making higher comprehension allow more xp expenditure per practice without making it more efficient is the way to go. In other words, if you have comprehension > 100%, it loops calls to practice() until the comprehension % is expended. That way it will make learning “Faster” without making it “more efficient”. Anything involving “free xp” is going to heavily unbalance the system, and make it basically mandatory that characters have a certain baseline intelligence (or equivalent with traits).
I think the grindiness of downtime is a mostly separate issue, but also in need of being addressed. What do you think about making reading into “read for X time” instead of “read a book”, “read a book”, “read a book”, etc…
Also, possibly add activities that are “fun” in order to pass time? Ideally it’d be something that is fun for the player too, so it wouldn’t be just another grind, but I’ve noticed before that your options to keep yourself entertained are pretty one-dimensional (basically reading or drugs, bleh). I’m afraid I don’t have any concrete suggestions for this, what WOULD one do to pass time in the apocalypse?
I like GlyphGryph’s suggestion (and Soron’s modification to it) to have skill books intrinsically lower xp gain. This would also raise the value of the mostly-useless “just for fun” books as they would have a morale boost with no associated xp gain penalty.
Speaking of morale boosts, I agree they seem rather out of hand. I haven’t looked into it closely enough to have an opinion on what to do about it.
Skill rust also needs some tweaking, I just looked into it in detail, and it’s negative skill gain with a rate based on skill level, so you have to be gaining skill fast enough to offset it, which isn’t particularly subtle. I’m thinking of modifying it like so:
Add a “last practiced” timestamp to each skill.
Update this timestamp each time a skill is practiced !!successfully or not, xp available or not, active or inactive!!
Rust with the current algorithm, but based on the difference between “last practiced” and “current turn” rather than purely based on current turn.
This should greatly, greatly reduce the intensity of skill rust, and is how I assumed it worked in the first place.
The only real down-side is it breaks save compatibility, but that’s still frequent enough that it really doesn’t matter that much.
Something else I’ve been pondering is adding a “high-water mark” for skills, and giving a bonus to comprehension when current skill is lower than that mark. That’s not as simple and obviously correct as the above change, so it needs more work. That having been said, I’d merge decent implementations of either of the above immediately 
