TwoSix
Everyone's literal second-favorite poster
I would also point out that we can't really draw a one-to-one equivalence between attacks, saves, and skills. A +1 to hit is worth more than a +1 to damage. A +1 to damage is probably about equivalent to a +1 to saves. And a +1 to saves is worth more than +1 bonus to even several skills. (I mean, just as an example, Jack of All Trades is a nice bonus for bards, but no one is dipping Bard 2 just to get it.)This is great progress! We need to remember that the player choosing the ASI is very likely to apply it to something that will benefit them. For example, although +1 prepared spell might seem circumstantial, it will be relevant a very high proportion of the time - maybe even 100% - for players choosing Intelligence. Similarly, the player choosing +2 Dexterity probably is using a finesse or ranged weapon that benefits fully.
For that reason I believe we have to assess it at say 5 circ. = 4 always. Essentially, asserting that 80% of the time the circumstantial is relevant. (Multiclassing unlocks excepted ofc.)
[Edited. I believe 5:4 is the largest discount that makes sense, for reasons [MENTION=205]TwoSix[/MENTION] outlined.]
Fundamentally, combat ability is worth more than the other pillars (and even if you believe otherwise, that's the balance point the game must consider), and a bonus to something you're good at is always more valuable than a bonus to something you're terrible at.