Not good to hear sending the device to HTC is sometimes less than helpful, but I guess if the device fails their tests they'll fix it.
According to these Sprint help pages, without insurance or their repair plan, they don't owe a customer anything. Not even free processing of a manufacturer warranty issue.
How do I replace my device under the manufacturer's warranty?
How much will my repair or replacement cost?
In the event of a problem, sounds like the $55 is the most hassle free method when you don't have insurance or a repair plan.