Though you're probably just used to how slow it is now, which is fine as long as you never spend any amount of time on a new machine. Shit gets addicting.
No, I happen to be a professional, I know what does and does not impact performance of a computer. My work laptop is a 6 month old Dell, and I would rather work on my 6 year old Mac.
Just about the only time that you will notice ANY type of processor lag is when you have run into a situation where you have topped out a processor for an extended period of time, this rarely happens for common users. The vast majority of even old systems do not max out their processors on a regular basis, unless they have been owned and someone else is using your computer to attack other systems.
Anyone who has a dog slow system, do not take my word for it, run the diagnostics, what is your processor utilization, is it pegged at 100%. Check your memory utilization, is it maxed out? Addressing the problem that is not your bottleneck will not reward you with considerably better performance.
Faster drives give a lot more bang for the buck then extra processor for most users. If you want to splurge get a SSD instead of a hard drive, which will allow programs and data to load much faster, and heaven forbid you get yourself into a heavy swapping state, then the SSD will be able to push data in and out much faster than a traditional laptop hard drive.
EDITED TO ADD:
For the vast majority of laptop users, the comfort and usability of the keyboard and touchpad will turn out to have a larger impact on the usability of the system than will the processor for the next three years.