I'd say in the 60s it was the main draw for the characters, but ever since the 80s the characters and plots have been much stronger.
And ironically, that's actually a complaint that a lot of people have, in that since the 80s, the actual musical aspect of the franchise has taken a backseat to everything else, including character development and storytelling.
The thing of it is, prior to the 80s, there was a time in television and fiction in general where character development was actually discouraged, mainly because in those days, nobody really gave thought or concern to continuity, so if characters remain the same, then shows could be seen in reruns and syndication in any order and there wouldn't be any noticable differences in the characters. This was especially true for finales: back then, shows were always discouraged from doing proper finales that wrapped up the entire series for fear that it would kill any chance the show had for an extended life in syndication . . . and all because THE FUGITIVE did this, and that apparently dug the show into its own grave.
I digress, though. Character development did wonders for the Chipmunks and Chipettes, because they all started out as flat, one-note characters, and they all eventually became more rounded, fleshed-out, fully dimensional characters with believable/relatable personalities.