Post: #1

Even if the stalwart administrators continues to block and delete the bot's spam, i think that this is a "losing battle" .

My suggestions

1-Block the wiki account creation, if someone want to register he has to send an apply/email to one of the administrators.

2-If someone want to register, he must confirm the registration by email(actually the email is optional, maybe this option will not block the spam entirely but it will reduce it I guess).

Post: #2

My suggestion:

Install TitleBlacklist Extension and get it running.

Create MediaWiki:Titleblacklist page with this line:
.*[0-9]+.* <newaccountonly>

This will counter almost every bot's account creation (works more than fine for me). Although some Bots might slip through, but that's something to get along with then.