Why should I bother, my last water heater lasted 20 years?

That's impressive, but not uncommon for older water heaters. The older water heaters purchased in the 1970s and 1980s had much thicker steel and more porcelain than today's units. Because manufacturers have cut so many costs from the manufacturing process, most steel water heaters made today will not last much longer than their warranty. It's much like the automobile; the thickness of the metal on today's units is very thin compared to older models.