Benefits of better cables with limitation of basic speaker wire in wall

I have a dedicated home theater, and as is standard most of the speaker wires are in wall with plugs to connect.

I have found that "everything matters" in terms of cabling and wires etc.  But I also have found that the system gets "limited" by the worst component and in this case it would be the feet of wire in the wall. 

My question is has anyone upgraded speaker wire/ interconnects and noticed an improvement in sound quality.  Also understanding that any upgrades are much pricier than hi-fi since we are talking 11 channels of speaker and connection on both sides of the wall.

Thanks for your thoughts