If you use spreadsheets, it is worth the money.
I have never really used spreadsheets for much since high school, but found that once I tried Numbers for Mac, I was using them for several different things.
Numbers makes spreadsheets easy for those of us who aren't exactly proficient with them, and is a beautiful tool for those who are. You have all of your work automatically updated in iCloud (If you want) so your revised spreadsheets are always available on any iOS device.
It's great for invoicing, balancing budget/bank accounts, exercise logs/journals, and so much more. Again I haven't been using spreadsheets very much since high school, but have found a new interesting them since getting Numbers.
FWIW I also have Pages, which works equally as we'll, but I don't use it nearly as often as Numbers.