I'm sorry it took me so long to get back to this. I think the indicator would only be needed if you didnt' have a tutorial and/or help guide/menu showing the keyboard commands and mentioning that you need to hit space to continue or what ever it is. Being told every time isn't really necessary for most people as long as they are told up front and can look it up if they come back to the game and have forgotten.
One more thing to look out for that I missed before is visual puzzles. If you have a puzzle that can only be solved visually, that can be a big problem. But it seems like you guys are really on top of things already! :)
Thank you for your solid work on this! You are a good example to others.