I've never used Versions, and the extra step needed to Save as are enough reasons for me to downgrade to Snow Leopard.
Is it possible to disable Versions in all apps and have a Save As… menu item instead of a Duplicate one?
I guess you're rather referring to Autosave. This post describes the difference.
To disable Versions, I posted the (maybe risky) procedure here:
However for Autosave the easiest work-around might be to use "System Preferences" → "Keyboard" → "Keyboard Shortcus" to define a keyboard shortcut (I used ⌘ ⇧ S) for the programs that have Autosave support and the "Duplicate" option in the menu:
For Textedit it will then look like this:
So you would press ⌘+⇧+S, which gives you a new duplicate window and then ⌘+S to save as new filename.
However, you original document will also (continuously) be saved and end up in the state where you created the duplicate - and without Versions (or Time Machine) you won't be able to recover earlier states as soon as you close your original document or the program.