Cool! I happen to be anti-spoiler so I appreciate it. I would suggest an alternate method (since you were kind enough to ask...): Can the text be embedded in a window that expands out when clicked? Or pops up?
I saw this on a web page that reported a general error, and if you clicked the text it would show you the full error. You click again and it disappears. It may require more scriptwitchery than the forum structure allows, but that's my suggestion.
My reasoning is this - maybe I want to read the spoilers but I don't necessarily want to post "Yes me too" just to see the spoilers. Plus, once someone posts, they might find out everyone else has been saying the same thing when the spoilers appear.
Don't get me wrong, I think your idea is a great way to start, elegant in its ease of implementation. Better than me holding a hand over a paragraph, dropping my Cheesy Poofs all over my screen while I try to scroll past.