Take a card like Born Aloft, for example. It's a Tactics card, but it's 0 cost. So, my interpretation is this: You need a Tactics hero to play this even though it costs 0.

At least this is how I've been playing these.

My reasoning is that if it's meant to be played by any anyone then it would be a Neutral zero cost card, not Tactics.

Which is a real shame...because I find Tactics to be the weakest link and I currently run a 3-color deck that doesn't include them, but Born Aloft is such an amazing card(Gandalf loves it!).

your interpretation is correct.

That is how you play zero cost cards.

The rules actually specify it on pg. 12, "Cards with a cost of zero do not require a resource to be spent in order to pay their cost, but they do require at least one hero under that player’s control to have a resource icon that matches the card’s sphere."