My Wireless Signal is 65% at the moment, but for complete satisfaction for my Nintendo Wii and Computer, I'd like it to be 80% or higher?

Is there any way of doing this?

Yes, use a repeater. Some routers can be set up in this mode. D-Link | Welcome has a few. You did not mention the wireless technology, so I cannot suggest one. e.g. 802.11 b/g or n.

I was thinking of an Amplifier? Also, I know it's foff topic, but I'd like to make YouTube Videos load quicker, will I need a Dual Core Processor for this?

There are two ways to increase signal. One is a repeater. The other is an antenna. You can load balance two internet connections or get one with a higher bandwidth to increase load times. The registry entries for XP actually slow the internet connection down. They do have to be changed when you have > 10 mb/s bandwidth available.

Your Internet connection is only as good as the pathway all the way through. If the other end has a bottle neck, then it will not matter what you do. Starting with faster bandwidth at your end is at least something you have some control over.

Try the Cantenna (Google it). It is a home made wireless antenna that can boost signal performance and distance.