Let's look at Sanity : what does it measure? A character's mental stability and capacity to withstand psychological trauma? Let's say that's our working definition of it. Why is it not a resource, then? Like HP. See something you can't rationalize? Roll Intelligence save (to use D&DNext parlance). Succeed, and walk away unscathed (or less scathed, depending on the genre you're trying to emulate), fail and suffer the loss of San points.
As for Luck, I could argue that Action Points are a partial reflection of that, and have been present in the game (if not always as a default assumption) for two editions.
So yeah, compared to Strength (physical strength in D&D being a massive abstraction), or Constitution or Dexterity (relfexes, hand-eye coordination, fine motor skill, all things that don't necessarily come in a package), they are very narrow.
Subsystems are cool, I think, but with six ability scores already, I feel you can do more with different resources for PCs to use than trying to cram more into an already crowded box. At the end of the day though, D&D is better served with a unified mechanic, and subsystems that plug into it to complement it.
It kinda does. Ever been rock-climbing? Part of developing the skills to climb rocky surfaces is developing the strength, endurance, and muscle memory to perform the task. In D&D-speak, being good at climbing (AKA having ranks in the skill/being trained in the skill) should mean you have the strength to practice the activity. In reality, from 3rd edition onward, if you roll up an 8 Str rogue, that skill rating is going to suck proportional to what it should be (and compared to a 2nd edition thief, for exemple).
The intersection of physical stats and skills is where it's most obvious, but even with mental attributes it can get wonky.
Ah yes, an attribute presented in a non-core rulebook, referenced a few times, and then dropped from the following editions sure has endured the test of time...
The problem with comeliness is the same as with every other ability score : what does it represent? With strength, you can have an objective reading, and say it's a general measure of muscle strength. But "beauty" really is in the eye of the beholder (no pun intended). Assigning a value to something wholly subjective is, in my opinion, not required for a game (and hasn't been required by the game since 1989, or really ever when you think about it.)
Not saying you can't make your game work with those (it's obvious you probably do), but assuming those as default assumptions in the core game would be a mistake, in my opinion.
I can work with or without such expanded ability score use, but they tend to be favored by players. Sanity, an overall measure of mental stability, is a lot of fun.
