Are you serious? Apple went from a single core A4 to a dual core A5, and thus multiplied not only processing powers but also cores, made multitasking much easier and saves on battery life plus the obvious performance gain. Graphics also experienced a 9 times faster upgrade. Crappy front and back cameras? That's the main reason most people are changing from iPad 1 to 2, I use facetime very frequently.
Look we can go on and on over whether iPad 2 is "better" than iPad 1. Yes, iPad 2 is faster, "better" than iPad 1.
But we need to take the OP's situation in hand. They already own an iPhone 4 for "facetime". So having facetime on the iPad doesn't add much value to the OP.
Duo core is great. But unless the operating systems are optimized for duo cores, you won't get full utilization of both processing power.
The big gain as you stated is really the graphics power of the iPad 2.
Most people who owned an iPad 1 and upgraded to iPad 2 are like me. I sold my iPad 1 months ahead to subsidized my upgrade cost. Or they just gave their iPad 1 to a love one. But it's not an "essential" upgrade.