The Macbook is due for an update, despite what the buyers guide says. Since its release it has been updated twice a year - once in the spring and once in the fall. You just have to look at the numbers and you can see that the Macbook is past its average update time, not mid product cycle.
As for whether to go for the 2.0 or 2.4, most users won't notice the 20 % processor advantage, and if you need to look at the keyboard, you're doing something wrong. If you do a lot of typing, whether in the dark or not, you would benefit greatly from learning to touch type. Check out
http://www.typingweb.com/, it's free. And once you can touch type, whether a keyboard is backlit or not makes no odds.