it seems we have come to a disagreement.
Spike has a decent amount of Development as a character, and has a fairly defined personality.
Thinking of him as the Servant of Twilight is a bit..... idk..... not right.
It more along the lines of Spike is a little brother to Twilight.
Basic Personality traits:
He is childish.
This is apparent in his B-day episode primarily.
He is in general freindly, but can be skittish at times.
Although not greedy in spirit, he shows signs of his Species greedy traits multiple times.
Hes much younger than most other characters in the series so it is kind of unfair to say he has No development.
Give him time. Im pretty sure he will become more defined in the future.