The crystal dragon only drops a few crystal every 5 days, whereas the goblins are ready for collection every 8 hours. The goblins have a chance at spawning other goblins which can be any or all of...
Lots of reasonably priced items this sale. I'm even able to complete max levels of some energy droppers. I'll have to wait for more info on some other items though, however the bear-on could be fun...