So often games, especially RPGs, have attributes and abilities that have a cost to acquire, but no significant cost to use.
One of the prime examples is Vampire: The Masquerade - Bloodlines. It has a great system of non-combat attributes and abilities. The game world is filled with gates that require a minimum level in one or more attributes/abilities to pass it. It is a lot of fun.
The problem is that once an attribute/ability is upgraded to a certain point, the player can pass any gate that requires that level. Escalating requirements mitigates this, but the game hits a ceiling near the end where it can’t keep relying on that mechanism and instead falls back on combat. The combat system is mediocre but does scale better.
And part of the reason for that is the combat system relies on resources, where the other systems don’t.
A more robust solution is to abstract skills from their use and rely on Resources.
Actions require specialized resources to perform. Skills do not directly apply to actions, but instead determine resource maximums and how well the character can acquire particular resources.
For example, take the classic RPG persuasion skill. Normally, the persuasion skill is a numeric value that determines whether certain social opportunities are available to characters. It is a Boolean condition where the character’s persuasion value is either high enough or not high enough.
Instead, characters can have a persuasion resource. The persuasion skill determines both the maximum persuasion units the character can have at a time, and determines how well the player is at acquiring more persuasion units.