Look... the objections to Contact Other Plane are bullshit. I'm just going to call it like it is. Either you don't understand how we're talking about using it, or you're being dishonest.
The spell has a 90% chance of giving you a correct answer, and nothing says you can't use another divination to ask "Are the answers I got on my last Contact Other Plane reliable?" Hell, you could even cast the exact same damned spell again, and go ask a different deity the same questions. That would increase the success rate to 99%, and you could use a third single question divination to ask "Which of the two previously cast Contact Other Plane spells is reliable?", or some such crap. It isn't even hard to come up with an error checking system for this, so I'm going to assume that you didn't even try, or bother to read those that have already been spelled out in previous debates about this shit.
And as to "attacking the wizard while he's casting it..." he'd know you're coming, because of the last time he cast it. He doesn't wait till the predictions from the first one have "expired" before casting it again. He casts it again before he is vulnerable. So he always knows exactly when someone is going to attack him, and exactly how best to defend himself against their attacks and WTFPWN his attacker. If he gets an answer of "you'll be attacked when you next cast Contact Other Plane"... he'll just take some motherfucking precautions.
And here is a simple set of questions that I came up with in like 2 minutes for how a mage could figure out exactly who is going to attack him for the next week, and how to best stomp the crap out of them. I'm sure someone with freakin' godlike intelligence the likes of which the real world has never known could do a lot better...
[spoiler]1) What is the first name of the enemy that will be the biggest threat to me in the coming week? (Let's say the answer is Bob)
2) What is the last name of the enemy that will be the biggest threat to me in the coming week? (Let's say the answer is Smith)
3) What is Bob Smith's biggest vulnerability?
4) Which of Bob Smith's capabilities poses the biggest threat to me?
5) What is the best way to counter Bob Smith's biggest threat to me?
6) What day will I face Bob Smith on?
7-12) repeat 1-6 for the second biggest threat of the week.
Continue this line of questioning until no further threats are discovered.
Then ask things like "Other than the threats I've uncovered today using Contact Other Plane, are there any other defensive measures that will be critical to my survival this week?"
If answer is "yes", then "What is the most important of these defensive measures?" and "What day should I take this defensive measure on?" "At what time should I take this defensive measure?" (Repeat for 2nd most important defensive measure, and also for offensive measures)[/spoiler]
So... using this one spell, the wizard is always going to know exactly who is coming after him, and what spells to prepare and strategies to use to defeat them. The only way this ever fails to work, if the wizard is using some error checking divinations to make sure his Contact Other Plane spell gave him the correct results, is through divine intervention (also known as the DM being a dickhead).
The only way to beat Contact Other Plane is to use it yourself to counter the other guy's Contact Other Plane, and then things get complicated as hell.