I think it is very important, and also not important at all. It's strange that this thread has come up, I've been thinking about this over the past few days.
On one hand there are those that would say that Tarot is essentially a Rorschach test of sorts; whatever you see in them then that's fine and there are no right or wrong answers. On the other hand there are those that would say that study of the symbolism is paramount to understanding the very nature of Tarot and that anything less is meaningless.
I guess I would fall somewhere in the middle. I do somewhat take issue with people saying "it's all intuition, it's all good" since in a sense that's cheating the deck maker of their intentions. Like books, Tarot cards are open to a variety of interpretations, but I think that those interpretations ought to be grounded in the source material itself, which can be varied. If anyone thinks that, oh, I don't know, The Catcher in the Rye is actually a book about Martians taking over the Earth, that's fine, but I expect them to show me, to prove it to me, text in hand. Just saying "it's my opinion and that's what my intuition tells me" isn't enough, and, again, cheats the author of his work.
So it is with Tarot cards. You can go as deep as you wish into the symbolism, but one of the things that differentiates Tarot from other divination systems is exactly that, the system. Some decks are more comfortably read from an intuitive standpoint alone, like the RWS (which is itself rife with symbolism) but others actually do need the legwork to really get all you can out of them.
On the other hand, it can be dangerous to get bogged down in to much symbolism. What Umberto Eco calls Salgarism, going off on tangents that have nothing to do with the issue at hand, makes for a dull reading. The person in front of me wants to know the answer to something, I won't spend three quarters of an hour explaining the origins of the Orphic Egg to them, obviously.
Ultimately, like I said before, in Tarot you can go as deep as you wish into the symbolism, but the deeper you go, your readings will, in my opinion, be that much better, since you have more "meat" to the card, more stories to tell about it. However I have received fabulous readings from people who never studied any of the symbolism at all, so maybe I'm wrong. That's just what works for me in reading, and I do think my study of symbolism has made me a better reader.