There isn't a good way to detect "nonsense" nicks. You or I could tell just be looking at them, but try to put that into some kind of matchtext and it's virtually impossible. You can take care of some situations, such as those with no vowels, or similar. However, there just isn't a good way to detect all "nonsense" nicks.
The only real good method is to just let them join for awhile to find a pattern on your channel and determine what is significant about the nicks and/or ident of those who are causing trouble in your own channel. For example, my channel was getting a ton of nicks that had a female name followed by 2 digits (supposedly an age) who were doing porn ads. Knowing how they worked, it was possible to set it up to ban any nicks matching that situation. But that's my channel. Different channels and networks have different situations.