Both of these cards were among my favorite cards when the Invasion block released. Urza's Guilt (Planeshift) still remains a favorite! I love the art use it for some gaming profiles. I sometimes make 3D Abacus Life Counters and am contemplating using foil versions of this card to make one for myself. This card was used in my Discard deck. If I was able to set it off with Megrims on the board, I would do a minimum of 8 damage, but many times this combo just won me the game!
Urza's Rage (Invasion), on the other hand, obviously went into my Burn deck. The Kicker cost is really steep and I don't recall successfully meeting the requirements for it often. If I was, it was likely in a Blue/Red Burn variant, since it allowed me to build up mass quantities of mana to cast larger spells. Three damage for three mana isn't the best, but having that Kicker ability is a sweet bonus when able to manage it!
I have foils playsets of both Urza's Guilt and Urza's Rage, so I'm all ready to rock. Unfortunately, neither fetch a large price, maybe $3-$5, while regulars are bulk rares. I don't believe either have any competitive appeal, so they will likely stay where they are on the charts.
Have you ever played with Urza's Guilt? What about Urza's Rage? If so, what decks did you play them in? Do you have a favorite Discard and/or Burn deck staple (or non-staple)?