...If you're an apple fan wanting to play with the DP, then no its probably not worth paying the price for a developer's account with apple
If you have spare $99 bugs, I'd say go for it.
Otherwise: NO.
That's the bottom line. You're dropping a c-note on a developer preview. If you want spend that much money to play around with go for it. In the past (except for SL) upgrades were costing around 125 so in theory you could save some money if apple follows that path. If they don't, you run the potential of over-paying for the OS