But the internent speed will see no dif? Ok I think I got it. What about things such as netflix load times? Buffering times? Like YouTube and etc? Amazon movie downloads? I don't do much file transfers between devices.
It won't help with any of those issues. This is assuming your existing 802.11N router is working properly and you were getting a decent signal to those devices.
If the signal to those devices was borderline, often a more modern router with better antennas etc can help.
If your existing router is getting a decent signal throughout the house and you don't plan to do much with wireless network transfers, there really is little reason to spend the money on an Airport Extreme. You would be able to attach an external drive to the Extreme and use it for Time Machine backups if that is something you want. Or your could just buy a Time Capsule.