One other suggestion: If you *like* any of the CrunchBang looks, such as how Conky looks, or the panel (tint2), or the Openbox menu/key bindings, you can just copy the configuration files to a USB drive (I would rename them!), them copy-and-paste things you like from those into the configuration files that come with the app when you apt-get them. They will need a lot of work anyway, so that is a good starting point. The Openbox autostart would be good to get, too, as it should have entries for starting Conky, tint2, and the wallpaper app (though CrunchBang may put them somewhere different, I dunno).
Also, I think you can steal menu items from the Xfce menu (sorry, am not in my Mint Xfce, can't check, and I just do them from scratch--using a 'CrunchBang' Arch I built atm). Or, there is a program that will generate them for you, and yet another that lets you edit in something considered more user-friendly than XML (though in my one time using it, it didn't do a good job, so I just edit the XML directly). As far as wallpaper, you can use nitrogen or feh, and pick you a nice minty one!
A couple of things about editing. First, convenient things: In my experience, you can edit conky live; just make a change and hit save, and it will refresh. Also, assuming LMDE Xfce uses gedit, it highlights code, making it easier to edit XML code (I am sure there are dedicated editors for XML out there, too).
Downsides: Getting things the way you like will almost certainly take a lot of fiddling, at best. At worst, you can mess up one of the Openbox config files (either for menu or general configuration, the rc.conf file) even very slightly and Openbox will lock up. Then you have to find a way to get out of the X window so you can edit the offending file (I usually use the power button, but there is probably a gentler way). Having Xfce makes it much easier to fix than on my setup, as you can log into Xfce and edit the file with a graphical interface (I have to edit using a text editor, as I only have Openbox).
So, getting there manually would be a fair amount of work, but you would learn a lot, and have a system that was the way you wanted. Plus, you would be using a Mint distro as your basic setup, so would have the Mint folks managing the updates/upgrades, and perhaps have a more stable system than using Crunchbang Waldorf, while having a real rolling distro, instead of having to reimage with a new testing when Wheezy moves from testing to stable (great point by rhodry!).
Hope this helps in some way!