I had a Kindle w/ keyboard and broke it. Replaced it with the Paperwhite. I would not say it is worth it to upgrade until you absolutely have to. My K2 was perfectly satisfactory, even though I had to use a little clip-on light at night. However, the Paperwhite was a good choice for replacement (even though the lighting is not as even as it looks in the ads). It will be nice not to have to replace those little batteries in the clip-on light every few weeks.
With all that said, I MISS my keyboard and buttons!