Yes, this is quite intentional; I designed this action key to behave exactly like the left mouse button, in all circumstances where the mouse button would be used (Except during text input while typing a save filename, since that could potentially be buggy, hence the explicit test). It's utterly wonderful to have an alternative to LMB when selecting items in a menu, for example (As in, move mouse over a menu item and press spacebar instead of clicking). I noticed this being used in a game called Aquaria, and it helped my carpal tunnel with that game significantly. 

Ideally, yes, the game would have a keyboard-only sort of mode, where everything (including menus and the like) would be controlled with the keyboard, and on mouse movement or keypress it could toggle between this mode and mouse-only mode. I was trying to figure out a way to properly get, say, Rarity's special power working on a keyboard with that sort of setup, and it would be less than ideal, so a keyboard-mouse hybrid is likely the best we can do there. Not to mention that all the code to draw the look at/investigate/talk to icons is entirely within the MouseHelper class itself, so I'd have to either rewrite all that or warp the actual mouse to nearby objects as Twilight walks around... neither of which I found to be a particularly good solution either. Of course, you'd have to do all this if you wanted full controller support, but this didn't seem terribly worth it for me to do, as I don't game with a controller often, myself.

What I suppose I'm getting at in a roundabout way is that a key to advance dialogue is great, and keys to move around are even better, but there's still a lot of clicking involved in this game even after all that. Clicking that I'd rather do without entirely, for wrist pain reasons. In my mind, using an alternate key (In my case, spacebar) as LMB is a really intuitive and great solution. I suppose I could create MouseHelper duplicate functions in KeyboardHelper, and dig through every single source file, adding tests everywhere where mouse functions are called, but this in my mind was easier and more direct (not to mention easier if you extend mouse functionality later).

Thoughts?