Err, what? He's changed and in fact it was Buffy that was instrumental in him seeking a soul. The biggest change a vampire could possible achieve in the verse.
But not that big of a change for Spike, was it? You know what would be an actual change? Throwing Buffy out of his "life".
I think getting a soul constitutes a far, far larger change imo.
No, thats only because YOU appear to have a big bug bear about him being with Buffy I'm afraid.
It was a huge change for Spike getting a soul; and it would be - not an actual change, but a big one, to throw Buffy out of his unlife.
The thing is - he still loves her, and she finally wanted to have something with him.
Now, if they break up, I wonder if Spike would like to keep living in the same building or even in the same city Buffy lives. He tried that, and it was working - he finally was getting over the idea of being with her romantically. But if they split, I believe it would be harder for him to be in that state of mind again. Then, he would have "to throw Buffy out of" his unlife.
Deep down he still wants to hunt and kill, that's how Archaeus got to him. He's still obsessed with the same Buffy. He still hangs out with the same group of mortals despite still having nothing in common with them. And he still doesn't give a piss about Wood's mom! So where's that big change?
Look, I want Spike to be awesome. Turns out, being with Buffy turns him into Riley. I want the chain-smoking, passionate and cocky yet likeable bastard. I want him to surprise me, to try new shit: new situations, new people, new lovers. I want William to be more like...Willow, actually. Huh.
You know what I think is the issue here? I like Spike, you like Spike/Buffy.