Should I attempt to upgrade or buy a new laptop?

You know it's time to get a new computer when it can no longer do what you want it to do, and it's often not worth the money to upgrade a laptop (desktops are much easier and cheaper to upgrade).

But since you say you don't do anything that requires that much computing power, that doesn't fit your situation. If you're taking it to a Mac tech support, they should be able to replace the missing keys without too much cost. But I would suggest learning to clean up your own "junk" and learn basic computer organization and maintenance.

But then you're complaining about the weight, and the only way to resolve that is to get a smaller laptop.

So that answers your question about getting a new laptop.

How much does this thing weigh? I went on Apple's site and found (sorry if I'm wrong) that the G4 iBook weighs about 6lbs - no light weight, but still no fatboy either.

You can upgrade many things but you're probably stuck w/what you have - not sure what you're trying to upgrade. If you go to the store, they will try and sell you something - but they don't have super powers, so you won't end up buying anything you don't want.

I've seen replacement keyboards on eBay.

it depends on the specification of the laptop