Only a wizard without a friend in the cleric business would ever bother with this spell. The risk of being reduced to a village idiot for a few weeks is simply too great, even when it's only a 5% chance.
But occasionally you need to ask a question without involving a cleric (especially if it's about a cleric). For those times you can sequester yourself in a nice safe spot, get a friendready to cast Break Enchantment (as if wizards had friends) , and expose yourself to the outer planes in a quest for knowledge. I can imagine times when doing so makes sense.
But I can't imagine any reason to ever contact the Astral plane. You have a 44% chance of getting a correct answer and a 32% chance of getting a lie or a random answer. How does that help?
Think about it this way. If I tell you a fact that is 50% likely to be true and 50% likely to be false, how much information have I given you? The answer is not 50% of a fact, or 25%: it is none. You have no more information than you did before you asked the question. An answer that is just as likely to be false as to be true is not an answer that is half-likely to be true: it is a random answer. And if I wanted random answers, I could just roll some dice.
Now, if you could ask the question over and over again, until you had a statistical distribution, then you could extract some information. But the spell pretty explicitly says you can't do that.
Contacting greater deities reduces the chance of misinformation to 10%, which is almost low enough to tempt a player into acting on the information. Notice I said a player; an actual wizard, with an INT of 20 and a career successful enough to get him to the point where he can even cast this spell, would never take such an ill-considered risk. Any question that can only be answered by gods is going to have supreme consequences for getting it right - but that invariably means there are dire consequences for getting it wrong.
The problem here is that the game designers simply didn't understand basic probability (or risk vs reward). The spell should have a 10% chance of failure at the lowest levels, and at worst a 1% chance at the highest levels. This might actually tempt a wizard to take a risk. As it stands, the only people who would act on information that is just as likely to be false as it is to be true don't need to fail the save; they're already drooling idiots.