Those cards are pretty weak in draft alone, but Tough Cookie can make them worthwhile until their self-sacrifice abilities are used.
However, you are also given the option to destroy cheap non-Creature, non-Land permanents
Keep them sealed if your main goal is collecting sealed products, but remember that condition, set popularity, and scarcity matter
The commander version of casual rares and mythics follow the typical price trajectory of newly release cards - starting off high in value, usually pre-selling for at least half of their original versions, and then dropping in value as more and more commander decks are opened
The flashback cost is among the lowest possible, and you can even use a summoning sick creature to pay for it
Another option is to have Sauron, the Necromancer be your commander, since the Nazgl are his servants