Sylvan Library is both way overpowered, even from a Legacy standpoint, and the wrong color for the effect.
This card is so good.
Legends copies are about to "Price Step" (http://urza.com/blog/ashnods-altar-and-price-steps) to $70-$80 apiece for LP/NM copies. Try to get these, soon, around $40.00 apiece. NM copies are pretty well picked over, but Heavily Played and Moderately Played copies can be snagged around $30 each, if you hurry. Personally, I prefer heavily played old cards to pristine new cards, but three other printings are floating around...
4th and 5th Edition copies are also surging, but not as explosively. Grab these at $15 or under if they're in LP condition or better. In a few years, I could see this up around $50.00 even for these "worst" editions. I see this card moving much like Blood Moon: too powerful to stay cheap and it would shrug off reprintings. It has one modern reprinting in Commander's Arsenal - stay away from this copy, though, as it's comparatively ugly (the original art is so iconic) and already over $100.
Just another Old Guard getting a promotion.