There are some key advantages to the Core I7 platform you should understand.
1. It will be able to drive any GPU setup now and in the future, especially multi-gpu setups.
2. You have to consider the time/effort required to rebuild a Core 2 system/AMD system in the future whilst a Core I7 system will be current for a little longer as it has up to date technology.
3. With a Core I7 you can be GPU agnostic, meaning you can run powerful AMD or Nvidia graphics card setups, you're not locked to one particular GPU maker if you want to run a powerful system.
4. A core I7 system is only a few hundred more expensive than a top of the range Phenom system and yet it you get the advantages above.
Some other things you should consider. Its more expensive in terms of time and effort to update a CPU/Motherboard than it is to update your graphics card. You can easily go through many more GPU upgrades than you do CPU/Motherboard upgrades and thats considered the ideal way to do things. Your GPU should last you between 18 months to 3 years whilst your CPU/Motherboard should easily be good for 5 Years.