Unless there has been more information shared about the property since last August, we don’t know what all of the differences are between Interactable and Active other than what was mentioned by the Roblox Staff Member in the thread for Release Notes 589.
I haven’t done any testing for that before but I’d imagine that could result in a very very very very small performance boost. It probably wouldn’t be significant enough to be noticeable unless you had tons and tons of decorative buttons, but it’s something that would be good to try anyway since it would also offer a clearer indication as to which buttons are meant to have functionality and which aren’t while you, or anyone else you may be working with, are editing the game.
However, if it’s completely meant for decoration and not meant to appear like a button to the player, it would probably make more sense to use a different GuiObject such as a Frame or a TextLabel, but of course it depends on how you’re utilizing the non-functional buttons for your game.