Everyone's perception of "f***ing huge" is different I guess. Although, yes the minimum width in 2011 is more than twice as big as the one in 2009.
Windows overlap though, you could just have your IE/media window overlap on the right half of Messenger's window and have practically the same result as you have before.
As far as Messenger Plus! having any feature for this: not for changing the minimum width. However, if you are into compact things you might want to check desktop contact. In the Plus! settings go to Appearance > Desktop Contacts. This is a per contact thing though, not really intended as your entire contactslist. There have been a few scripts which mimic your contactslist in a minimalistic way, but no native Plus! features.
I though A-Patch used to have an option to remove minimum width restrictions (or maybe MessPatch?), but currently not for WLM 2011.