There’s another way to look at this:
Let’s assume with your numbers that it will be around 5500$ to rebuild gyros and replace vacuum pump. Let’s now assume you take that 5500$ and put it towards the installation of a dual GI275, which is on the high end. The cost of the two GI 275 units is about 8500$ which is your net cost.
Now what did this 8500$ buy you over and above your existing system? GPSS (GDC31) will cost about 4K installed. This leaves 4500$. How much does a backup electronic AI cost. A G5 backup AI is 3500$ installed. This leaves 500$. Realistically it doesn’t because 5500$ for installation is on the high end. But even so everything else the GI275 gives you like dual ADHRS, reversion and redundancy, alt preselect, backup gps, dual battery backup, about 40 pounds weight loss, etc etc etc is worth way more than 500$!
I agree that you can save the 8500$ and the airplane will fly just fine but when comparing costs it’s not apples to apples.