I've never thought Buffy could pick it up because it was mystical, but I never thought it meant she was very much stronger than Spike either. I do think it was played for laughs, but that doesn't discount it. I like Stormwreath's meta on the subject, and his conclusion that Buffy's strength changes based on what is needed for a given situation. With a vampire, she is stronger, so that she can defeat him, but not much stronger. With five vampires, she is much stronger so she can handle that. With the troll hammer, she had enough strength to lift it, but in actuality this was much more strength than Spike actually has, because vampire strength doesn't fluctuate. In all honestly, I think this is probably just an explanation for the writers' inconsistencies in storytelling, but I like it.

I also like the idea that vampires are faster and Slayers are stronger.

(I haven't responded yet to the post you are referring to, I may copy this response and reuse it).