iWork could be worth it for Keynote alone, if presentations are your thing.
Numbers is, in my opinion, much better than Excel for general spreadsheet tasks. It is based around a slightly different paradigm that I find makes for better organised data. Lots of people prefer the Excel though, so I guess it's 50/50.
Word is far better than Pages.
You can always give the iWork demo a go and buy based on that. That'd be my recommendation.