Ah, the great season 6 debate: Was Spike after his soul, or not?
I think he was: From the "




is gonna see a change," to "give Buffy what she deserves," I think he started, fought, and received what he wished. When he spoke to Buffy in Season 7, (episode where Spike was being manipulated to kill people), he told her that she should get over her self-centeredness, because "the soul I got for myself."
I think by "what she deserved", Buffy needed another champion, with the ability to do good; not a chipped lapdog. He got tired of being conflicted, not quite monster and not quite man, but he could never go back to being completely as he was; it wasn't the chip that changed him - it was Buffy. He'd do anything, evil or good, for her, and proved it many times in Seasons 5 and 6. In my estimation, love for a woman changed him, and respect for the woman made him decide to regain a soul.
But that's the beauty of those last two episodes in S6; you could read it either way; Either Spike was being noble against type, or he's lying or deluding himself right now. The trick is, we won't know until Shanshu actually comes to the fore, again.
But I still stand by the fact that Spike is different from Angel in his desire, and his focus. Angel over time, has lost both, and I think a big struggle for him this season will be regaining it.