This is a bad idea.
Minor exploits might be ok to play with, but once all the easy stuff is found, what happens when users are playing with the site in such a way as to harm the experience of other users?
Who gets to wade through all the "lol, I used a userscript to change the logo, gimme the hacker badge" and "Hey, I found that if I send thousands of requests a second the server stops responding, gimme a hacker badge" messages?
This is not behavior we should be encouraging. The awesome software and network engineers at Stack Exchange are sufficient to the task, and we shouldn't encourage another thousand or million people to perform random attacks on the site in the hopes of exposing a weakness.
Further, who gets to wade through all the "lol, I used a userscript to change the logo, gimme the hacker badge" and "Hey, I found that if I send thousands of requests a second the server stops responding, gimme a hacker badge" messages?
Lastly, while being proactive about exploits is generally a good thing, it's possible that there are hundreds or thousands of tiny little things that could be better, and verifying a given problem, and fixing it takes resources that are better spent on features that will positively impact the site. Yes, we can fix that last 1%, but it's going to take months of man hours for work that ultimately isn't going to improve the site as much as putting that same effort to work on other features.