* Gracious: "Gracious" is more about quality of character and demeanor. While you could use "more gracious" and "most gracious," those forms are less common. Instead, we usually use synonyms to express different degrees of graciousness, like "kind," "courteous," "polite," or "generous."
* Hilarious: "Hilarious" means extremely funny. It already implies a high degree of amusement. While you could use "more hilarious" and "most hilarious," they're not very common. Often, we use synonyms like "side-splitting," "gut-busting," or "hysterical" to express different levels of hilarity.
In short, it's more natural to use synonyms to express different degrees of "gracious" and "hilarious" than to use their comparative and superlative forms.