How to Combat Psychic Answers?
I don't believe we need to.
How can we encourage detailed questions?
I don't think detailed questions can be encouraged any more than they already are. Yes, we could make the instructions in the right hand column blink...
...but that won't work either.
I think the best way to deal with this is to let the person post the question, and then let the community assess it. Some of them will just shake their head and move on. Some will ask follow up questions. Some will downvote. Some will vote to close. Some will take what little information they have, and attempt an answer.
I think this is great! If we give a shotgun approach to a new question, then something may well hit the target, or the community will eventually reach a consensus on whether it should be closed, edited, or downvoted into oblivion.
Regardless of what happens, the person who asked the question gets a lot of fast feedback. If the issue is important to them they will engage the community and the question will be fixed, and the answers will get better.
If they don't engage, and the question remains broken, then it doesn't hurt anyone to have some wild-guess answers floating around, some of which might help someone else with a similar problem later, searching google for similar terms.
How can we encourage users to post comments asking for more information rather then pointless answers?
I don't believe this is necessary, and in fact it's a good survival trait to approach the problem with some guesses even when it's not clearly defined.
I've seen several questions where the OP responds to the guessed answers with additional information that eventually fills the whole picture out, but they did not respond to direct questions in the comments. Some people simply engage differently.
From their perspective they ask a question, and all they get in response are more questions. What they might prefer is a few answers that may be wildly off the mark - they may know immediately that they are off the mark, or they may try it out and come back with more information. Regardless, this is how they engage with others.
It's not necessary to discourage people from trying to solve a problem when the issue is not clearly defined.