It's really a coin toss, Sarge. It never hurts to have a backup copy of your favorite pistol. But it also never hurts to have a 9mm AND a .45.
The Glock 30 is one of my favorites. Amazingly accurate for its size, and soft-shooting for its weight and power level. It is somewhat thicker than the 19 and will generally need different holsters and magazine pouches. You'll also need extra magazines, of course, and the ammo is more expensive...always a consideration with a budget to stick to. Another G19 will work with the same holsters, mags, and pouches you've already accumulated.
Frankly, I don't think you'll go wrong either way.
Don't mean to seem indecisive; it's just that it's too close for a third party to call.