You need exactly as many tools are necessary to do the job of the game. Different games have different jobs.
D&D is fight-porn and wish fulfillment. So you need tools that allow for 1) tactical and 2) totally awesome combat, plus rules that allow for lovingly crafted butt-kicking characters.
Then, because people find fantastical heroes demolishing stuff to be more meaningful when there's a plot, you need a smaller amount of rules to help you craft plotlines.
That's it.
For other games, things may be different. D&D doesn't need extensive rules for insanity, because its not a big part of the game's goals. A Lovecraft based game does need extensive insanity rules. A Lovecraft based game, by contrast, would actually be harmed by the amount of combat rules D&D has, because combat isn't the point of the game. D&D style combat in a Lovecraft style game would function as a morass in which the game drowns.
Genre mixing belongs in supplemental books that openly admit that they're attempts at genre shifting. Done right, these books not only provide additional rules to add things like extensive insanity systems to your game, they also admit that they're changing the underlying goals of the game, and suggest edits to already existing rules.
D&D is fight-porn and wish fulfillment. So you need tools that allow for 1) tactical and 2) totally awesome combat, plus rules that allow for lovingly crafted butt-kicking characters.
Then, because people find fantastical heroes demolishing stuff to be more meaningful when there's a plot, you need a smaller amount of rules to help you craft plotlines.
That's it.
For other games, things may be different. D&D doesn't need extensive rules for insanity, because its not a big part of the game's goals. A Lovecraft based game does need extensive insanity rules. A Lovecraft based game, by contrast, would actually be harmed by the amount of combat rules D&D has, because combat isn't the point of the game. D&D style combat in a Lovecraft style game would function as a morass in which the game drowns.
Genre mixing belongs in supplemental books that openly admit that they're attempts at genre shifting. Done right, these books not only provide additional rules to add things like extensive insanity systems to your game, they also admit that they're changing the underlying goals of the game, and suggest edits to already existing rules.