If you are on Yosemite there is no urgency to move to El Capitan as the big feature jump was Yosemite, but coming from Mavericks there were some new bits worth getting. The need to keep up to date is not part of the past Apple culture.
The ZX81 - that was considered the height of modernity and luxury back then compared to the stuff we started on - colour, and remember the screen flickered every time you pressed a key. But it was the 1st affordable 'micro' computer of that era dominated by Commodore Pet, Apple II, and Tandy TRS80. Then the Act Sirius one with MS-DOS changed everything 12months before IBM launched the PC which was technically inferior at every spec level to the Sirius One. The rest is history, but the likes of Altos, Fortune and CT were fun along the way. The world nearly spun off its axis when the daisy wheel printer was replaced by NLQ matrix and Laser printers (i.e. the word laser from si-fi movies instilling a sense of ultra modernity and star wars, flash gordon, etc). Memories . . .