So, secret rare cards are usually more valuable than ultra rare cards, full art cards can be more valuable than holos and so on
It usually sells for somewhere in the region of $100 but it seems that Charlotte Katakuris card is rising in value somewhat
They often reward you for casting instants and sorceries, drawing extra cards, or chaining spells together, which fits perfectly with the Izzet Guilds fast, experimental, and explosive style of magic
(more) Thomas Mak Wins YCS Chicago
This question actually caused quite a debate here in R&D
The right play is going to depend on the matchup (if they're a very fast deck it could be right to block), your hand (if your next play is a Ghoulraiser and your creature is instead a Walking Corpse, it is excellent to block), and your tribe along with your deck