Going from 512MB to 2GB, you should notice startup and programs start quicker. Going from 1GB to 1GB+, you will only notice a very slight increase.
By full power. I mean by default on laptops the power settings are for Portable/Laptop. Right click on the desktop, click Properties, Screen Saver, Power... Your power scheme will be on Portable/Laptop (meaning it's not using full CPU power). If you plug it up on a AC adapter at home, set your Power scheme to Always On. This is will use your CPU power, just if you go mobile with it, set it to Portable/Laptop, otherwise the battery will only last about 2 hours max.
Dell should have a Help/Support page for drivers for your laptop. Windows Update may have some of them, but they could be outdated by a version or two. Windows Update is slow about getting up to date drivers.
I would recommend this:
Create a System Restore Point
Run Disk Cleaner (More Options, System Restore, Clean up) Not many do this and it does up a lot of space over a period of time.
My Computer, right click on C: (or main drive), Tools, Error Checking, check both, Start (reboot) This is will take sometime (don't be in a hurry for it).
I recommend running CCleaner once a week (at min.) and do the System Restore clean up about every month. Defrag about every month if you are a heavy user. Do Error Checking about every 2-3 months.