I can honestly empathize with you as I've been the financial clerk in my ward for 6 years. For me, the one thing I truly enjoy about my calling is knowing that my kids see me return to church every Sunday to count tithing. I want them to see me serve and sacrifice my time for the Lord, and since I've been doing this so long, it's pretty much all my kids have known me to do.
True, this really isn't a calling where you can experience spiritual growth, but I have received blessings, and I would be willing to bet you have as well if you would look for them. Just remember that the Lord called you to this calling, and he knows what you're capable of. If you get burnt out, maybe ask the ward clerk to sub for you for a week to get a break.