I recently sent a request into Evernote via customer service. In order to get this issue more attention, and make them more likely to add the "Add to Dictionary" feature back, please use what ever channels of communication you can to politely request the feature back. I explained to them there are a lot of industry specific words I encounter, and it gets difficult or at the very least annoying when my notes are filled with tens or hundreds of "mispelled" words. Remember to state your case calmly, clearly, and politely.
Thanks,