You can't get the halloween spells anymore. I'm not sure about the x-mas ones though, haven't noticed if the dude is still standing there, or if he even is, I don't know if he'll still give the quest. My opinion though is that it was a waste of time, plus I got killed trying to do the quest. There is no benefit to it, plus I actually had people I was grouped with complain about being small. There was no xp awarded either, lots of running, really just a waste of time. Of course that is just my opinion.
If you decide to do it, if it's still avail, GL
Oh and I'm not sure they'll do anything for valentines day, they might, I just wouldn't bet on it, they didn't do it for every holiday last year. Ooh, thinking about it now, they could do something cool for fourth of july, fireworks !!!