I wish to add that mostly those Multiple Domains Crowding spammers wouldn't be satisfied to occupy one or two of top 10 spots on first page of Google Serps, they want to occupy all top 10. When those "smart" spammers occupy most of top 10, it wouldn't harm them much if one of those Google algo updates kill the ranking of one or two of their spam domains.
Those spammers work on complicated mix of domains they purchase or lease which are just slightly different in look and feel. I think it is safe to consider those spam domains as "Doorway Domains" that are created for the sole purpose of manipulation of ranking on Google Serps. As such, those "Doorway Domains" used in Multiple Domains Crowding spam are neither adding much value to Google Serps nor Google users.