I don't think wikification is an appropriate action here. Basically, community wiki is used for answer posts that get edited a lot, get edited by multiple users, or denote that a post has substantial contributions from multiple users. For a discussion of what community wiki means, see "What are 'Community Wiki' posts?" on Meta Stack Overflow, and Grace Note's post on "The Future of Community Wiki". The issue you're raising is not collaborating, but similarity, possibly verging on duplication.
I'd definitely leave the second and third questions on your list alone, because they don't duplicate anything, to my knowledge.
There is an argument to be made that the first and fourth questions on the list are duplicates. I hesitate to flag them as duplicates because there are eigenvalue algorithms out there that are not Krylov subspace methods. If someone can make a persuasive argument with some references that says that the only fast algorithms to find eigenvalues of a matrix in an interval of interest are Krylov subspace methods, then I'll mark the fourth question as a duplicate of the first (or vice versa). However, lacking a broad understanding of the different types of eigenvalue methods out there, I'd rather leave them alone until someone makes that argument.
