Great advice Surry!
A faster drive will always speed up a system ...
You might even look into the new "hybrid" drives. They have a solid-state (static RAM) drive as the primary, caching over to the physical hard drive, any files that are not being frequently accessed. This improves performance "and" gives you more space.
My issues with the RAM were when I would run "virtual systems" on my PC. When running Windows XP or LINUX, or especially Solaris, in a virtual session, the system would just begin to "BOG DOWN" big time! One reason was because I only had 4GB of RAM. The 16GB of RAM I now have is fantastic on the speed! I can be running multiple screens, and a virtual system alongside my MacOSx and it never breaks a sweat!
With VirtualBox, you can "tweak" the RAM available to a virtual system.
For instance, Windows XP can only recognize 3GB of RAM - "max". So, that's all I give it!
The others, I tweak them as needed, usually giving them 4GB, but I can actually go 8GB if I want and still have a full 8GB for "me".
I strongly urge the upgrade of the RAM ...
and just as with the many things people have been "jail breaking" the iPhone for have since been added to the iPhone repretoir (and vice versa), I think Apple will soon open up the ceiling here, understanding that there are "power users" who are now giving their hardware a second look.