I've been one of his biggest critics in the past but now that he's playing a deeper, more disciplined role (i.e. staying out of the final third), Gana has comfortably been our best midfielder.
Most of the time, we're playing something like a 4-2-4 (2-2-6 when we get close to the final third) and that setup doesn't work defensively unless Gana is putting out fires all over the place (see Spurs for an example of what happens when we play that system without him). Plus, despite his limitations as a passer, he always makes himself available for the ball and is willing try things when nobody else is. It's actually kind of embarrassing how often Gomes and Sigurdsson lay the ball off to him when they have time to to turn and get their heads up and look for something better.
Committing to a proper 4-3-3 should actually solve our problems. I think most would agree that Chelsea was our best performance this season. Consider how much deeper Sigurdsson defended in that match. I'd argue that that was the key to our success. Swapping a second forward for another proper midfielder should help us restrict space in the middle of the park, which forces our opponents wide more often (generally leading to poorer attacking opportunities). It should also help us generate more counterattacking opportunities, which will suit the pace and directness of the front line.