For me, it's not a specific time in which I buy new magic products. I wait a long time, maybe a year or about 9 months (Christmas time or Birthday). I occasionally purchase some decks of cards, but that's for practicing purposes and of course performing purposes. For right now, I try to create or think of new stuff, rather than wait for something new to come out from either E, t11, Penguin, or any other place. I don't give into the hype they set for new products. It also might "look" cool, but maybe the method is impractical or that the trick itself just doesn't fit my style of performing. I would just go by what you're into and if it fits the category. If it's something that would fit great, and when I mean think about it I mean actually think about it by reading other reviews first. That's how I decide when to purchase new material, but other than that I practice what fits me already or try and create something on my own.
Cheers,
Casey Rudd