Realistically. Think scruffy Clive Owen hair.
Granted, I agree that Reeves has limited emotional range and that he isn't a fit for the character, but I completely disagree with how you seem to interpret Spike at a fundamental level.
To save myself and others here in the forum a ton of time, I'm not going to go into a long diatribe about how he isn't really in emotional pain, and that he doesn't "rage" against anything, because explaining it will take all day.
In summation, he's more listless than anything and exists in a dreamlike haze since the person he lived for is gone, and to mischaracterize him as some brooding angstpot who just wants revenge against Vicious seems to me, completely false.
The running theme of him being a wandering ghost seems to have been lost to some, and I don't really see how (look to the entire point of Knocking on Heaven's Door for the thesis of this theme).