For 5 mana, you are able to drop a multi-colored creature onto the battlefield for the cost of only a tap and 2 colorless mana. If you need another way to cheat Dragons into play, this is definitely it.
Interestingly enough, you'd expect a card like this to be bought out at some point with the amount of casual appeal it should have. The best Dragon cards, in particular, are multicolored. But you don't have to play Dragons to make it work. It can be any multicolored creature, and there are plenty of them out there. A mere 5 mana investment is easily worth what this card can do.
There aren't too many EDH / Commander decks that can't use Dragon Arch. With Wizards printing many powerful multicolored creatures in recent sets, Dragon Arch makes cards like the Tarkir Dragonlords and other splashy bombs that have multiple color symbols in their casting costs a lot more palatable to play. Yeah, there's plenty of artifact removal out there, but you only have to get one or two high powered creatures out into play using this card and it's well worth the mana investment.
As of November 2018, this card typically retails for about $4 USD with foils selling for roughly 5 times that amount. During late 2016, Dragon Arch foils hit nearly $17 on average before falling to around $10 by the beginning of 2017. They approached $20 again by the end of 2018 You would think that a card with as straightforward a power level as this would be gobbled up by casual players and Commander aficionados everywhere. While some foil copies have certainly disappeared, they are still out there to be had.
The most valuable cards in Apocalypse, outside of Vindicate, have been reprinted at least once. Dragon Arch has not seen a reprint, and it likely won't see one anytime soon. If you want a copy, you should pick one up before it suddenly gets bought out and the price skyrockets out of control. Dragons are always going to be popular, but this card only needs multicolored creatures to be good. Those are always being printed, so this is a great artifact to have in your collection.