Rare cards annoy me. It always seems like I could assembled my supreme deck if I just had a few more rare cards. In my mind, each rare card equals $$. I could continue to tell you what I think, but The Ferrett wrote the definitive primer on rares.
In Defense Of Rares
To a lesser extent Mark Rosewater (head card guru) wrote articles explaining card rarity.
Rare, but Well Done
One of the reasons why I wrote MTG Forge is because I wanted to use rare, fun cards. So I guess without rares, maybe MTG Forge wouldn’t ever exist, who knows? Much like being mana screwed, rares are a part of Magic.
(Mana screw is a really unnecessary part of the game. You should be able to play any blue card and it would magically become an Island like the Marvel/DC VS card game. I might implement this as an optional feature in MTG Forge.)