I have a late 2009 "Whitebook" that I dropped an SSD and 4gb ram in years ago.
It does Office365 (word/excel) pretty well, Garageband (altho loop selection takes a while because I have a lot on there), and it can surf/email. Honestly, I never really got (maybe I'm doing it wrong?) the people that have 40 tabs open in their browsers... I have one for Pandora, then one for the site I'm surfing...
I also have WindowsXP running in Bootcamp to control my DSLR and Celestron telescope. I've pushed mine to the limits, and while not a total rocketship, it still does what I need it to do. (gets about 2 hours max on a new battery)
I'd say if you can get the upgrades relatively cheap, might be worth doing... if it's more than a few hundred, like others have said, probably best at looking for a 2011+ model.
--rob