True. I didn't explicitly mention it, but I meant using standard/approved methods, such as generating the legit commands:

CREATE LOGIN

EXEC sp_addlinkedserver

etc..

With the old master db there, you could get (almost) whatever you needed from the existing master.

You could specify the sid on specific SQL users if you wanted to keep those the same, reducing the need to "re-sync" native SQL users as you restore/attach user dbs.