Is there any way to create hundreds of new sites at once, by importing data from an Excel spreadsheet? (E.g., one field is the title of the page, another is the content.)
No, no automatic ( with excel shets) is possible for such a sensitive action.
Yes, with the coming - payable- "Pro - account" is a manual "cloning" easy and possible.
No, there is a limit of 20 "free" sites per account ( no way of "hundreds").
Yes, the limit will be higher for "pro- accounts".
No, I do not understand why you need hundreds of sites. Google and other search machines are going to ignore a spam-technic with links and infos.
Yes, all this is possible if you make your own server (and "wikifarm") with the open source version of wikidot.
Hope this helps?