Yes, doing this kind monthly premium pass will help retaining players for TE as well. Plus a relatively small but very steady income stream.
(usd $5 or equivalent really is not a lot for most - players who like a game a lot would gladly pay up that kind of amount to help support the game)
The premium benefits is about right for now. If it is too much then it could put off too many non-paying players, which would in turn hurt TE pockets from digital income stream.