Another reason to replace old Eichler glass is because of safety concerns. Tempered glass, or "safety glass," which breaks into small pebble-like pieces when struck, has been used in cars since the '20s, but was not required in 1950s-era houses. The Eichlers were built with glass that breaks into potentially lethal shards upon impact or during an earthquake.
However, this can be prevented with a properly applied window film at a cost far less than new glass. (On the peninsula, Sun-Chek is a good resource for questions about this product: 650-965-7730, www.sun-chek.com.) As a bonus, the film also reduces heat gain and blocks ultraviolet (UV), which can cause fading in fabrics and some flooring surfaces such as cork tiles and carpeting. Note that window film does not increase the R-value of glass, while some replacement windows do include UV-blocking capability. And keep in mind that acrylic inserts make original Eichler glass safer for those inside the house.
Replacing your original Eichler glass offers many benefits—perhaps the opportunity for year-round comfort the greatest of them. However, whether the cost is worth the benefits is a judgement call that homeowners have to make for themselves.