I recently switched to Elementary from Ubuntu as day-today distro. But I'm not able to use alt-spacebar menu, if I want to maximize or minimize the window. It's just I hate going over arrow keys. Yeah! Long time Vimmer! Thanks.
Try disabling Alt-Spacebar as a hotkey for toggling maximized or any other entry, this should revert Alt-Space behavior to what you are accustomed to.
By default for me Alt-Spacebar was mapped to Next Keyboard Layout in Keyboard > Universal Access, by disabling this the window menu took over properly.