IMO, it doesn't matter what Spike went to do. It can be read both ways, and it still works because by the time Spike gets back to Sunnydale he already has a soul and as such isn't capable of knowing exactly what it is an unsouled vampire feels, because the soul messes with everything.

It only matters if you're an unsouled Spike redemptionist, and that is something that wasn't going to happen in BtVS, the writers didn't want it to happen (rightly IMO).