Like me, I sometimes cross-post ideas in different groups and then if there's enough interest, I'll set it up as an official event in the group that I host.
Without the email notification, it will be impossible for me to keep track of the interest to the idea.

I think it should be an option, same as message board, for the person who posted to decide whether they want to track the msg / idea instead of taking it out entirely, also add the option for the poster or those who like the idea to stop tracking it as they want, just like the msg board now.