Yes, it's almost de rigueur for punk bands to start changing once they learn a fourth chord. Some manage it better than others, but as a rule punk and ability usually don't go hand in hand.
There are two British bands I recall, Action Pact and Dead Man's Shadow, who both when in a similar, odd way. Both started off as fairly acceptable, bouncy sort of UK 82 type punk bands (Action Pact were quite good actually), admittedly not thrash, but I used to have albums from them that were - weird, in that they were trying to play a more musical kind of music. It wasn't pop, it was sort of rock but more melodic. As a result, hardly any memorable actual tunes.
