For how ubiquitous and iconic Thirst for Knowledge is, it's a wonder it's still below a dollar. This will see more reprinting, but... by this point it is becoming partially immune. It has an unsmirched history as an uncommon, and at 5 printings, it's hard to imagine that even a release back into Standard would keep the price down, even in the short-mid term.
Thirst for Knowledge last saw a reprinting in Modern Masters 2015, with the Duel Deck artwork. Gotta say, I think this new artwork sucks, however it does feature Tezzeret, a multi-printed Planeswalker, which will draw in a lot of players. The Modern Masters 2015 Foils are the only Foil copies of this artwork available, and they're percolating pretty hard. They're still obtainable around $2.00 apiece. This is the best option for proportional gains in the short-term to mid-term.
Snatch up Modern Masters Foils up as a high-yield, short-to-mid-term, medium-risk spec. These will likely pop to $5.00 apiece within a few months, and have a good long-term outlook.
Now to the Mirrodin Foils (original printing), at around $8.00 apiece and clearly on the move. There is some definite room for big gains here. This is the iconic artwork, and this is the best long-term pickup of all printings of this card. These will see $15 within six months, and $25-$30 within a few years. The big spike a few months ago shows the space that this price is capable of carving out, if not yet quite sustaining.