When I am trading for cards, I follow one simple rule: Lose hot cards and add cold. Recently that means moving Advent of the Wurm into Steam Vents. Looking for cards that are cold means getting what others aren't interested in, often at a discount even to TCG lows. Having what everyone is looking for keeps people coming back to you when they need anything. Of course, this isn't all I mean by hot and cold.
The reason Steam Vents is a cold card is it once had a $20 price tag. Despite its versatility, it now languishes at all time lows. Compare that to Advent; a card that has yet to lose any value coming off release. Standard has plenty of reasons to like this insta-wurm: Augur of Bolas, Delver, Snapcaster and populate mechanics. I am not sure that is enough to bring Advent to $10, but I wouldn't bet against it. So why the heck am I trading copies away for Steam Vents?
When I want to price a card, I consider where it is and where it's been. That means ignoring a lot of new cards until the market has time to price them. When I see Steam Vents falling from $20, I see an easy 100% return on investment at current prices as a conservative evaluation. I need the vents $12 for that to happen and Modern season is catalyst enough to hopefully get there in a hurry. Advent is a $5 card for me, at best, until it gets to $10.
Right now, a bet on the Wurm looks more risky to me. I am not sure how playable the card is outside of Standard, a fact that puts an artificial time constraint on any spec. While Boros Reckoner shows that Standard alone has no problem driving up card prices there is too much uncertainty in cards that play in one format and have shorter price histories for me to not move into something more predictable.
To keep things simple for my addled mind I use $5 increments as price resistances and supports. I would read Steam Vents as up-side $6 (current price)-$20 (all-time high to nearest multiple of 5). The greater the upside, the less risk at current pricing. Compare that to everyone's favorite Reckoner $12-$25 and you'll start to understand why I assume the Vents are safer. For those keeping score Wurm has a positive value ($6-$5), and which a best means there is not enough pricing data.
I'm going to talk now about three different cards and offer my reasoning for specs into and away from those cards.
Scavenging Ooze is seeing an M14 release. That card will make Deadbridge Chant better in Standard and certainly will have a home in Modern. Instead of being seen as a positive, this reprint has NM copies available for just over $16 on TCG Player. Meanwhile, prices on Ebay remain around $20. With volatile pricing giving speculators plenty of opportunities to pick up copies under $16, the Ooze looks like a good bet for at least a 25% return in short order. The card's playability in multiple formats also adds a margin of safety other M14 speculations can't offer. COLD
Deathrite Shaman is around $10 again, and this before Modern Masters! Here is a card that will see play alongside Scavenging Ooze as well as offering a way to fizzle Ooze targets. Here is a card that will see play in every MtG format thanks to its synergy with fetchlands. Justifying a quick return to $15 isn't too hard on playability alone. I've actually got a $20 target long term for the Shaman, and know a good finish will push this guy to that level in short order. Right now TCG Player looks like the best place to pick these up online, and anything $10 or less is a snap purchase. COLD
Sire of Insanity offers a lower entry point. Available for around $2 on both TCG and Ebay, this card can be made too unsymmetrical in effect to ignore. Unfortunately, at 6cc the Sire is unlikely to be a 4-of in any serious deck list. Rather than looking to accumulate, trading copies at TCG mid offers a $2 return (assuming a low entry point). I like foil Sire copies, and trading regular versions 2 for 1 seems good to me. HOT
Finally, the easiest way to hedge your speculations is a quick check of buylist prices. The Sire is currently fetching a 2$ price from Cape Fear Games. With NM copies available on TCG for the same price (100% hedge), building a position is safe even considering a short price history. For comparisons sake, Deathrite is fetching $7 (70%) and the Ooze will net you 10$ (62%).