If you play 3D and HD quality games on a phone, edit HD video and photos, and do other intensive tasks it would be good to have a very fast phone.
But, if you just plan to use your cell phone as a phone to call and text people, browse the web, read, watch video, take photos and video, check e-mail having a super fast phone would make less sense, and current phones you can buy like the Samsung Galaxy S3, iPhone, HTC One-X, Windows Phone 8, etc would be good enough for most people.
I agree, phones would be faster when technology improves, but I wonder would speed be less noticeable for the common person like how a 10 dollar calculator is as fast as a 20 dollar calculator. After you are done typing and adding the numbers, the answer shows up in less then a second you press the [ = ] button on the calculator.
It depends on how you use your phone, if you mainly use it as a phone with texting and the occasional browsing, then no, but if you use your phone for gaming, browsing, and as your personal assistant to your daily life, as well as a phone, then yes, you will need more power to accommodate the added use on your phone.
