>>Year end tasks here include moving 2Y old mails into "old" folders, which grow once a year and are somewhat hefty in size. Then they are saved right away, so that for the next 12 months the newly arrived mails are in smaller folder/files (13 months worth in Jan, 24 in Dec) which can be backupped faster. Searching still easy if you organize the folder structure to easily drill down.
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>My work related email is in the inbox of the work related email account, and each year thereof is in a separate subfolder. In a few days from now, ctrl+a on the list, create new folder with 2013 in the name, paste, compact inbox, done. All indexed and searchable.

too lazy to create new yearly sub-folders here - just moving to a general "history". But my input is not as clean as yours - a biz related mail might creep in via other account and these must be preserved by law. Trying to cope with many half-spam folders filled by rules, which then can be blown away ;-)