Ashnod's Altar is a favorite of mine. It's my favorite creature-sacrifice outlet. It's in many of my decks. This original printing is still somehow only $5. I remembering seeing these for $5 apiece back in 1997 or so in a display case at a local store. This price has been very stable, a stalwart old guard that has seen competetive play forever in Vintage, Legacy and now Commander.
Ashnod's Altar is about to burst. Give it a month, maybe three months... These original Antiquities printings will be probably on the order of $20+ after the coming spike...
But refering to the now-familiar forthcoming price movement in Ashnod's Altar a spike is a bit of a misnomer. There may be some overshooting and restabilization of the resultant price, but the larger structure looks more like a step to a new equilibrium price of 3x or more. This was seen in previous articles about Island of Wak-Wak, Felwar Stone, Serra Angel, Greed and others. Price steps are a huge opportunity for the long-term investor.
This type of price increase is absolutely unprecedented in Magic, and the effect is slowly rolling over the entirety of the roster of old staples. This is not something that happens once a year, or once every 5 or 10 years. The current period of unprecedent growth (see http://urza.com/blog/mtgs-growth-whole), together with the spread of Commander (which uses Vintage cards) is causing across-the-board price stepping-up of most choice old staples. Even some useless crap is stepping-up in price, just due to its scarcity and to the continued, growing demand.
Reprints are just not keeping up with demand. The card pool grows, but not at the rate of new players or growth of interest. For Wizards, this is a good problem to have, and their response has always been the same to similar bottlenecks throughout history: print more cards.
Reprinting becomes more useful and less harmful as the game matures (at current levels). Consider the diminishing returns of the effect on the price of a reprint at comparable volume. A fifth printing of Ashnod's Altar will merely ding the price, and in so doing introduce newer players to the card, the net effect would be positive for the price (especially for the original Antiquities Edition). Eventually, reprints don't do hurt to the price of a card at all. Nowadays, Lightning Bolt seems to go up in price a few nickles every time it gets reprinted.
So hoard more old chestnuts.