While I agree with you that Caltrops in a Dom secondary is redundant and pointless, I think you may be missing the actual use of the power for a Blaster.  If you put the Caltrops BETWEEN you and the enemy and then attack from range, Caltrops will prevent, or at least delay, enemies from reaching you to use melee attacks. A single Slow enhancement is enough generally to floor run speed. It's an every spawn power for soloing certain playstyles.  
	On teams it's mostly useless, yes.