Nadu was also banned in Commander, so we can't even really discuss its applications there (not that that's my area of expertise anyway, mind you)
To assist you in establishing a price, look at the averages for comparable cards sold on the site Card Market
Don Andres, the Renegade Stealing cards from your opponents is cool and all, but what if you could get even more rewards
However, as mentioned before, the difference between the single mana cost of Stubborn Denial is significant compared to its Lofty cousin
Yes, keeping reverse holo Pokmon cards is smart, especially if you plan to complete sets or collect fan-favorite Pokmon
Another option for these creatures with the Ring tempts you triggers is to have ways to bring them back from the graveyard if they should die