The reason you can't find an online source (Edmunds, Kelly blue book, etc) for evaluation of the TE option is that 99% of potential buyers don't know what the Trail Edition is and don't care. Most 4runners never leave the pavement, so the TE option adds no value whatsoever for those buyers.
If you can find a buyer that cares, I would say it would add $1000 to $1500. The primary additional benefit is the rear locker, and you can add an ARB to a non TE for about $1500 if you do most of the work yourself.