Quite interestingly, a Blade Control deck in Legacy that placed 7th at a major tournament actually ran two copies of Back to Basics in the main deck. Likewise, Miracle Control, a three-color deck, has been running 2 copies in the sideboard on a regular basis now. The Enchantment really is that powerful and played at the right time can stall out a game that you may otherwise have lost.
Is Back to Basics really worth $20 plus? Probably not. Considering that you can get slightly played copies for around $15 means that the price should return a bit to normal. It’s also important to consider that Back to Basics is not on the Reserved List. While it’s unlikely that this Enchantment will be reprinted any time soon, it could be. If you need this card, I’d consider paying the lower price for the lightly played copies. If you want to grab them for speculation purposes, I’d probably hold off since more copies are being listed on TCGPlayer for lower prices as the days go by. $10 seems like a fair price for this card.