I'm afraid I can't help at all but wondered if you'd mind sharing the Dean/Spike story of which you speak? Seeing you mention this pairing really made me sit up and take notice this morning!! ;)

It's Running on Empty (http://virtualpersonal.livejournal.com/264514.html )
a WIP by VirtualPersonal. She has more Dean/Spike fics as well.

Title: Running On Empty (WIP)
Summary: After being rescued from hell, Dean is a broken man who is plagued not only by memories of the horrific things he's done, but also by lingering dark needs that he can't control. He can't sleep, for fear of the things he might do. He can't trust his brother, who has walked the dark side with Ruby. He can't feel, not when he's self medicating with liquor. For him, there is no hope, until he meets the vampire Spike under circumstances that might finish them both. Of course Spike could be Dean's own 'walk on the dark side.' Set in early season 4 of SPN.

http://www.tthfanfic.org/Story-24235/Cas+Running+On+Empty.htm

Here are some more

http://www.tthfanfic.org/Category-2-1552/Spike-Centered.htm

Have you tried 'Twisting the Hellmouth'? It's my first stop for crossovers with BtVS.
This should take you to a list of fics featuring Spike and Dean
http://www.tthfanfic.org/main.php?list=1552&full=0&character=Dean

to the moderators of spnstoryfinders: I have 2 more reply's in my mailbox, but they won't show here??