I like the idea, though if it became in widespread use, writers would do as spammers do--write to get past your filter.
One concern is that it'd be labor intensive for you to build up a large enough corpus with some metric to compare to so you know how well you're doing. Marking it by hand is labor intensive, and if you use a lot of humans, it might be a little inconsistent.
I don't think they'd do that. The purpose of the fluff is not (usually) to deliberately conceal their beliefs. It's there because it's what some people want to read. They want a candidate who "cares". I don't think the people who write the fluff would have any motivation to try to beat fluff filters.
Come to think of it, instead of trying to beat the filters, what if they specifically cooperated with them so that they'd filter out nothing at all? Think of what a great boast it would make: "I'll take you straight to the point, and these folks over here will prove it mathematically". I could picture Ralph Nader trying this.
I think they already do that. Those phrases on posters of politicians remind me a lot of the way I write my CV, inserting all the keywords that recruiters look for.
In fact, it probably would be easy to identify the best keywords for politics with Google Adwords, just see which ones get clicked the most?
One concern is that it'd be labor intensive for you to build up a large enough corpus with some metric to compare to so you know how well you're doing. Marking it by hand is labor intensive, and if you use a lot of humans, it might be a little inconsistent.