[Springtime]

> I prefer to retain the file's modified date when I just update tags so I'll know how old the rip is

Mp3Tag has a timestamp preservation setting. There's also the ability to run an external script/program on all selected files (via the Tools sub-menu of the context menu) or by configuring File>Export with a script.

For those wanting to preserve original timestamps I'd suggest storing them into custom tags in the files themselves as a backup. Mp3Tag can be set up to do this automatically using an Action (its scripting syntax). That way one can always restore them back using a script.