Really if you're just using it for access to the outsider's knowledge, you can at least try to summon an outsider with a very high knowledge modifier (high int,
Skill Focus, racial bonuses...). Not sure what standout options are there though.
However, if we interpret this spell a little less restrictively, we might be able to get the outsider we summon to use spells or abilities to help us answer our questions (such as anything that raises a knowledge skill, or perhaps even any spell that obtains information), and ask questions beyond what can be answered by a knowledge skill, such as where we might be able to find a person we are looking for, and have them cast divinations for us. In that case this spell is actually a pretty good catch-all information gathering spell, worth the component cost. The restrained take on this is that the outsider may do so of its own volition, but is under no obligation to go that far to answer your question. The less restrictive interpretation is that since we treat it like
Lesser Planar Ally (and indeed the price for services of that duration is the exact same) then if we ask for it to answer questions or gather information, it should perform that task according to its task and our request, rather than only rolling Knowledge or Diplomacy.
But there are other tricks that are possible with Planar Inquiry as well. If you call an outsider with Planar Inquiry, you can use your questions to pass information to the outsider, which the outsider might then pass on to a superior upon returning to its home plane. If you're doing a campaign where there is a deity with a vested interest in your mission, this can be leveraged for interesting consequences by utilizing an appropriate outsider as a messenger. Another stunt would be to call an outsider with a
Plane Shift spell-like ability and inquire about its willingness to aid you on your quest, basically working out a deal manually and then letting the spell expire, after which the outsider can Plane Shift itself to you. In addition, if it has a
Teleport spell-like ability, it can study the current location to teleport towards it afterwards.