A dedicated center channel does appear to make dialogue easier to hear , especially when you bump the sound level for that channel up more than the mains, so adding a center could be more beneficial than surrounds, especially for TV, although I love my full 5.1 system for TV, movies and music.

Jason
M80 v2
VP160 v3
QS8 v2
PB13 Ultra
Denon 3808
Samsung 85" Q70