Question: a few weeks ago, we setup a cronjob that wipes the entire contents of /tmp every Sunday at 5am. I wasn't really convinced that this is a good idea. Today we discovered that a certain task depended on an existing directory inside /tmp - the task was broken, and worse, it remained silence about why it failed. The question is:

Is it generally a bad idea to just wipe out /tmp?

Answer: 
It's not a bad idea to do something about stale old files in /tmp, but I'm not sure that nuking the contents is the best thing you could do.

My CentOS servers use something called tmpwatch, which runs daily and can be configured to remove only files that haven't been accessed in a certain period (30 days is a popular delay), or modified in a certain period; it can be told to leave directories alone unless they're empty, or not to touch directory files at all, or to exclude files used by a certain user (root is a popular choice).

This works well for me, and it offers enough hooks that you can tune it to do what you want. I'd recommend tmpwatch, or whatever your distro offers that's like that.
My thoughts on this is..

Yes.. dont wipe the /tmp..

Lots of strange and weird applications use the temp for buffering and temporary storage..

If the information wasnt important, it wouldnt store it there :)

Ive seen, logging buffers, webserver sessions and even library versions in there on servers..
Its best that you leave it alone.. unless it needs to be cleaned...

Hope this helps :)