It's definitely worth visiting. It has changed quite a lot of the past 5 or so years and there isn't quite as much to do as there used to be - sadly the 'dome' in which you sat down and experienced an overhead show of the patterns of the stars has long gone, but there is a 3D cinema (last time I went there it showed a simulated flight to Mars).
The only advice I'd give is to not view it as a full day out - maybe half a day at most - but you can take a long stroll through the very pleasant gardens next to the car park.