I played KH1 and KH2 without CoM as well. Playing CoM does explain things such as why Sora was in a deep sleep in the beginning of the game, and why Riku could control the power of darkness. But CoM doesn't have as much importance as it could have, seeing as how Sora no longer had any memories of anything that happened in CoM. Besides, CoM doesn't look that fun on the GBA.

Though it does look quit fun on the CoM remake on PS2. God, I do hope Square-Enix releases it and Final Mix+ in the West, no matter how unlikely it is.