Just for the sake of argument, I'd try to locate one of the .22 Conversion Kits. I'm also a Glock 19 guy and the cheapest ammo I can find is Federal 115 grain FMJ and they are $9.00 per box, still a lot more expensive than .22 ammo.
I have a Ruger MK III .22 and the earlier poster was right, it's not really similar to your Glock, the grip angle is more similar to the 1911 A1. If you can find a .22 conversion kit, you'd be spending more trigger time with your gun, the one you intend to carry on your person. I think the conversion of your 9mm to a .22 for target practice is a good consideration.
All that being said, having another gun around isn't all bad, either. if you found a .22 conversion kit later, you could always sell the .22 pistol to help pay for the cost of the conversion kit.
either way, it's a no lose situation. Good luck regardless of what you decide.