Here's the flip side of the coin.

What cards did you shun at first glance, but then end up noticing their merit later?

First for me, would be Mind Killer, the DE attachment

0 cost/ 2/5 loyalty

Attached character is -1 power.

A free way to render units in your opponent's kingdom/quest useless. Especially in the first 3 rounds or so, where those guys really matter.

Second would be Wake the Dragons, the High Elf quest.

2 cost/ 2/4 loyalty

When the card has 3 tokens, return a High Elf card cost 3 or higher from your discard to play.

Kind of cute, but pretty nasty when you realize this lets you play Gifts of Aenerion on every single opponent's turn until they snipe your questor.

How about you guys?

While I like the idea of this thread, the two cards you mention are hardly "underrated". I propose something else though:

Fledgling Chaos Spawn.

No power, only 1HP, battlefield only, minor damage effect. It does look questionable (especially compared to DE's Slaves, or Empire's Militia), but they do have a great use due to metagame: Every one and their grandmother plays Lobber Crew, and since Skaven are so great, Destruction decks are very common to begin with. The spawn makes your opening so much safer to Lobber Crew annoyance. You can sacrifice something you do not care about, and sometimes even kill a Spider Rider to boot.

Contested Stronghold

Probably people know, but do not write about it because it's so obvious, but a bit bland. It's a huge amount of hammers for just four barrels. Think of it as an Innovate every turn.

Kdansky said:

FCS works as blocker for Lobber Crew, but won't kick in its Forced when used in that role. FCS's Forced works when it is destroyed, not sacrificed.

Isn't destroyed a subtype of sacrificed?

FAQ:

"Destroy
Destroy means to put a card that is in play
into it’s owner’s discard pile. It is important
to note that sacrificing a unit is not
destroying it and vice versa."

Kdansky said:

How funny, that's the magic of different metas I guess. We're old Game of Thrones vets, so here, anything free and in-faction is a staple card for loyalty and fodder purposes alone. Thanks for the lobber crew tidbit, we don't have a very big playgroup, so I'll have to pass this along to our orc player and keep it in mind.

Also Contested stronghold is actually a little bit overrated here. Amazing ability, and great synergy with innovation, but as we've all started to toolbox in our support hate, playing a 4 cost anything so early comes with much of a risk.

HElves with Contested Stronghold(s) + Treasure Vault(s) is nice fuel for Bolt Thrower and/or Flames of the Phoenix + tons of units back into play.

As for orc lobbers: Most of us play all nine lobbers we own, quite often for 3 cost (due to zero other orc in many destruction decks). They are that good. We think they should be 2+2L or 3 + 1L. If your starting hand contains two of them, it's often game over right there, because you can totally cripple your opponent's economy by killing off his first two small drops.