How can I make a powerup increase a player's speed incrementally?

Got it. Here’s how I set a “pickup” in Blueprints before, maybe replace the Event and heck the collision of your pickup

On the object with Collision (my case, a static mesh), I set the physics like this

5299-screen+shot+2014-05-01+at+9.32.00+am.png

And used OnComponentDidBeginOverlap Event to trigger the logic

5300-screen+shot+2014-05-01+at+9.32.25+am.png