I don't really see it as necessary as a blanket rule. If you post a filter, you do it with the knowledge that you're sharing it with a friendly, acknowledging community. Anybody who plagiarises (i.e., adds very little to a pre-existing filter then resubmits) will be identified pretty quickly by an astute community, and anybody who adds something really special to a snippet is doing the community a great service, even if they needed a little assistance to overcome a hurdle.
I think if you want to submit a snippet and feel precious about it, perhaps put a "please attribute me..." etc. in the filter description? I figure that what goes around will come around.
I've made some filters that I really like, but if it weren't for the previous work of many skilled filter artists I wouldn't have been able to do it (at least not as quickly

) That's just the way things go, though. We get the privilege of saying that we were there from the Beta, and broke some new ground; but if our stuff pales in comparison to those who come later, I'm more excited than fearful - and I would like to think that's the general opinion.