I suppose the point could be argued either way but I still think you're "grasping at straws". Thanks for the friendly discussion though.It's canon that vampires take longer to heal from fire-damage. Darla and Drusilla were set on fire and took ages for them both to recover (comparatively speaking to vampires shrugging off other damage such as bullets and falling off of buildings).
So Spike gets crushed and burned enough for his body to only be slowly able to heal itself. In fact isn't his face a bit messed up/burned in 'Surprise?', that would explain it.