As Slartibartfast explains to Arthur, mice aren't just "white furry things with the cheese fixation" (that's Arthur's understanding of mice, 24.51); they are, in fact, "protrusions into our dimension of vast hyperintelligent pandimensional beings" (24.53). (Quick note: "pan" means "lots" or "all"; so "pandimensional" implies that they live on several different dimensions or on a higher dimension than we do.) They are the ones who build Deep Thought and order Earth so that they can solve the problem of life, the universe, and everything.
The mice also, as we learn, can set quite a table. When Arthur finds his friends on Magrathea again, they are sitting at a table "beautifully decked out with exotic dishes, strange sweetmeats, and bizarre fruits" (31.14). Notice how nice all that stuff on the table is: each noun (dishes, sweetmeats, fruits) gets an adjective to make it sound more special (exotic, strange, bizarre). And just in case we missed it, the table is described quite clearly as being "beautifully decked."
Yeah, the mice put on a nice party. This might seem like a confusing thing to do for mice who seem to be obsessed with big philosophical issues like the meaning of life. The answer is—you guessed it—that the mice aren't really all that obsessed with those issues.
In fact, the mice only get into the philosophy business because the question of life keeps interrupting their favorite game of "Brockian Ultra Cricket" (25.2). When it comes to Benjy and Frankie mouse, in particular, it's clear that they are not obsessed with the truth. They just want to come up with an answer so they can "do the 5D chat show and lecture circuit" and make a lot of money (31.58). So even when the issues seem big and serious, Adams reminds us that the people—or, ahem, mice—involved are foolish and absurd.