I drove a focus as a rental for a week last month. Going from the Sonic to the Focus "for more space" is... what are you talking about? The Focus is bigger on the outside but smaller on the inside.
(edit to add) I have a Hatchback Sonic, and drove a Hatchback Focus. Maybe the sedan Focus has more room... but then again the sedan Sonic has more room than the hatchback model. So, I'm still dumbfounded by the idea that you could move to a Focus for "more" space. I think there's technically .1 cubic feet more room, but it is so wasted in the design that it feels like there's about 2/3rds the space.
My Sonic is a 2012 so I can't talk about Mylink issues. Seems to me getting the mylink system fixed or replaced, for free, by your dealer, would be cheaper than going to a clunkier heavier car with less internal room, at what I can only assume is a costly trade, as you lost value on the Sonic the moment it left the dealer floor and the Focus is more expensive.
Not that I'm trying to talk you out of it or say you were wrong, cars are largely a matter of taste, and there was nothing actually wrong with the Focus, I just like the Sonic a lot better... as you might expect of anyone on a Sonic forum. But those two specific reasons, those don't make sense to me.