[charles Tauber]

Short answer: not likely to make a significant difference.

We know that a guitar that has never been strung will never need a neck reset: zero tension=infinite time till neck reset. We also know that many guitars will need a neck reset after 20 to 30 years when subject to standard string tension. We don't know what happens in-between those two data points.

Let's suppose, for discussion purposes, that string tension is linearly related to the need for a neck reset. With that assumption, you'd get 10% longer before you'd need a neck reset, proportional to the reduction in string tension.

If we assume your guitar might need a neck reset in 25 years, then, by lowering the string tension you might get 2.5 more years before the reset, extending it to 27.5 years.

Even at 25 years, with a typical glued-in neck reset being about $500, that's about $20/year spread across those years of its life. If the guitar lasts, 50 years, that's $10/year.

Anyone really concerned about the cost of a neck reset is advised to purchase a guitar with a neck configuration that is easily, and less expensively, reset - typically a bolt-on arrangement. Also, with the seemingly increased incidence of brand new guitars with poor neck angles, check the neck angle on any new purchase. Otherwise, you might be looking at a neck reset in the first few years of ownership.