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Your ranking strength is still available - it's just being held back because of some of your content. Either ditch the content that was hit or revise it.
I really don't think any of those things will resolve a Panda penalty / filter.
Of your content that was hit, were there many pages that honestly weren't good results for their rankings? I.e. were there better pages (more information) or more relevant pages (sites offering services instead of just information)?