Do you have a good engine monitor with 4-cylinder EGT & CHT? If so, and if you plan to fly the airplane more than a few hundred hours over the next few years, FI is the way to go imho. It will pay for itself over time. I was saying that when we thought $3.00/gal was expensive. Now, a year later, we think $5.00/gal is expensive. What will we think is expensive next year?
With FI you can balance the injectors (Airflow Performance can help you out with that), which means you can run LOP (lean of peak), which can translate to significant fuel $ savings.
If you don't have a good engine monitor & you don't want to do panel surgery, forget about FI (imho). Or if you only fly 50 hours a year or don't plan to fly more than a few hundred hours before you sell the plane, I don't think you'd ever reach the "paid for itself" point for FI.