With a 3/4-7 GPM pump I am guessing little to no irrigation, which would be maybe 300 gpd for 27 years, or close to 3 million gallons. That tank is about 3 times larger than what pump manufacturers would say is a "properly sized tank", which I am sure is one reason the pump lasted so long. That is also the way I liked to size tanks before using CSV's, if I could get the customer to spring for the larger tank(s).
In my area a 1.5HP or 2HP- 20 GPM pump is normal, with lots of mis-matched irrigation. That could be upwards of 12 to 15 million gallons in 27 years. You can't put in a large enough tank(s) to keep cycling on/off from destroying the pump prematurely, and half a dozen torque arrestors wouldn't be enough to keep it from whipping the wire. I have many of these systems with CSV's, a small tank, and no torque arrestors that are still working after 23+ years. I don't know how much longer they will last. But if a CSV made these systems last that long, they would certainly make a 3/4-7 with no irrigation last a long time as well.
Additionally with the really large tank the shower pressure would be descending from 60 to 40 PSI a lot of the time, while the people with a CSV and small tank are enjoying a constant 50 PSI all the time. It doesn't sound like much difference but a constant 50 PSI is much better shower pressure than when pressure is continually descending coming out of a pressure tank. And it is much easier to make sprinklers hit the target and overlap as they should with a constant 50 PSI compared to pressure continually changing from 60 to 40, 40 to 60 over and over.
But good job, 27 years is an excellent run for any old pressure tank only type system.