Lower traffic does not always translate to bad idea as it might be in your case. Having more specific words and long tail keywords also means that the person looking around might be more ready to buy than someone searching with your old set of keywords.
General trend is people are looking for infomation, they will be lazy and use the easiest words to search. If they are ready to buy they will get as specific as they need in order to find what they want.
Optimizing your site for the new keywords would make sense if:
- You are selling something rather than giving people information
- and if finding products and info is harder to find which I don't think it is in your case. The rarer the information, the more specific people will get when searching. So it would be good to rank for both shorter/broader phrases and long-tail/specific keywords.
