If you're still in the index, then sending reinclusion requests probably won't help you, because as far as Google is concerned, you're not being penalized per se, you're just not ranking well.
I believe that was true at one time, when Google only had the ability to deindex sites they didn't like.
I do not believe that is currently true. I believe that reinclusion requests are now the proper mechanism for penalties as well as complete deindexing.
Of course, I could be wrong. If I knew anything, I wouldn't be getting traffic only from visitors who had bookmarked my sites. ;)
Ah yes, here is a quote from Matt Cutts on this very point:
If you’ve been experimenting with SEO, or you employ as SEO company that might be doing things outside Google’s guidelines, and your site has taken a precipitous drop recently, you may have a spam penalty. A reinclusion request asks Google to remove any potential spam penalty.
Not that I have been doing anything outside of Google's Guidelines, but it appears that Google may believe that I have.
So yes, according to Matt, a Reinclusion Request is appropriate for penalties as we as for complete deindexing.