Well, wiki spamming is quite common! I ban about 5 users a day on my
Travian Wiki. It makes me mad, and sad, but it happens.
Personally, I would feel guilty breaking a wiki, but I guess others don't.
Because I am not big on blanking, I block those users for an infinite amount of time. If they just blank part of the page, I might ban for a few days or weeks.
If they make a small change, I might just change it back and post on their discussion page.
An easy way to change stuff back is to go into the history of the page and click on an old version. Next, hit edit, and then save that. It will then save the old version of the page to the database.
If I were Jordan, I would protect the main page so that at least looks good to newcomers, and then they can see the horrors of the spammers as they dig deeper into the depths of the wiki!
Overall, there really is no way to stop these spammers. You can require people to create an account to edit the wiki. This makes them think more before they act, but it still isn't spammer proof. Some people will still create accounts and get the account blocked. Your best bet is just to stay on the prowl. If you see an old page, revert it, or restore from the history. If you are a sysop or bureaucrat, you can also block/ban the user for a given amount of time.
EDIT:
Log into your wiki account
Next, click History on the left side
Next, choose an old version by clicking on the date
Next, hit edit
Then, hit save page
Your done!
Note: Sysops and Bureaucrats can do this quicker.
Note2: I did not actually perform this backup because I didn't want to mess up the homepage! This was only for demonstational purposes. I just did a mouseover of the save button, but did not actually click it. I clicked home instead, and then browsed back to GTP.
Also, for those of you that want to know who's banned, you can go here -
https://www.gtplanet.net/guides/index.php/Special:Ipblocklist