Well, a tower is a guy who keeps shooting or providing a benefit simply for existing. A trap would require maintenance. If you place a tower in the right spot, he can keep shooting people and won't get into trouble unless an enemy bumps into him while walking towards you.
If you're running, and you drop down a tower, he's going to get shredded before he even gets off a shot. The thing about the towers is that they don't have a very far detection range. The enemy has to be within a few spaces of them before they can see them, and by then it's usually too late.
A trap would cause damage to an enemy, but then require you to reset it. You could walk over it to fix it. Or dismantle it to reclaim your coin.
There could be interactions between traps and towers, with a tower who resets traps.
A bit of a shame about the fireball explosions. Thought that was 100% intentional.
The spread power up is good. It's interesting that firing speed and arrow speed are two different stats.