Do You want targeted traffic or targeted traffic? .org or .com does not make any difference to most advertisers. We want results!!! Period. As an advertiser myself, I could care less if it were a dot zen site as long as it consisted of visitors who were interested in my products or services.
The question I would be asking is would .org cause me to loose my serps. If not, what would be the benefit of changing it to .org other than status. You may want to get input from your current advertisers and see what their thoughts are.