Several years ago, we did a cruise on Carnival's Imagination. At that time, it was pretty gaudy for my taste. About two or three years later, after it had gone into drydock and had been refurbished, we sailed on it again. The tacky, gaudy colors had been toned down and it was much easier on the eyes. We've not been on the Liberty yet. We've booked a cruise on her for May 2012. We've looked at all of the photos and videos we could find on line, and I like the decor. I hope the decor isn't changed too much, and that the drydock is more for regularly scheduled maintenance and not a complete re-do of the decor.
As long as a ship is well maintained, I would have no problem with sailing on an older ship. While most everybody else is sailing on the new ships, maybe it will make the older ones a little less crowded. That could be a bonus.