Which ones? Almost no REALLY expensive part is really worth the money.
So, there are some of those pedals which are about 30 bucks which is a fair price for some good pedals, and then there are the sealed magnesium ones which are over 70 bucks. I wouldn't spend 70 bucks on pedals... Okay, maybe I would. But, I would want to have been riding for no less than 5 or 6 years and be able to do some pretty serious tricks first and already own a bike with other parts that are really good on it.
Things that are more important than 70 dollar pedals:
1. Good rims
2. Good sealed front hub.
3. Good cassette hub (street) or freecoaster (flatland)
4. Good handlebars
5. Good cranks
6. Good headset.
7. Good brakes
8. Good tires
etc., etc., etc. Almost everything on your bike is more important to have 'really good' before the pedals.
OH: If you ride flatland, the only pedals you ever need are KHE Stimulatorz.