I ride in the same area, same problem. If the hole in the tire isn't big enough for the tube to start popping through, you don't need to replace the tire (and from a goathead, it almost certainly isn't). If it makes you feel better, stick a little superglue in the hole. I don't know if it really helps, but in theory it will keep the hole from getting any bigger and keep other stuff like bits of glass from easily entering the hole and giving you another flat.

Last time i had Krylion Carbons on my bike the rear lasted > 2,500 miles. Your tires should have a lot more life left in them.

JB