Say what you want about Apple and price, but I've had PCs since 1994 and the two Macs I've had have (usefully) outlasted every other machine by quite some margin - this one in particular. 6 years without formatting a Windows machine (I can't talk for now, but especially back then) would be crazy.
You might want to consider running Manjaro[0] or Haiku[1] instead (I've had great luck with both on older MacBooks [2,3]).
Nessus reports El Capitan as a "Critical" vulnerability due to lack of security updates:
According to its self-reported version number, the Unix operating system running on the remote host is no longer supported.
Lack of support implies that no new security patches for the product will be released by the vendor. As a result, it is likely to contain security vulnerabilities.
...
Mac OS X 10.11.6 (intel) support ended.
Upgrade to Mac OS X 10.14 / 10.13 / 10.12.
[2] https://tinyapps.org/blog/201811010700_linux_for_2009_macboo...
It's not super easy to replace, but if you're comfortable with a screw driver, it shouldn't pose much of a challenge, and the instruction from ifixit are great.
I'm still holding tight to my 2012 MBP, but it's got a replacement battery, and a roomier SSD to breathe some new life into it.
I'm currently weighing up the option of installing Linux onto it as I'm more inclined to move away from the Apple ecosystem, but I have reservations on what that will do the battery life :/
I still own a MBA from 2011 in its original state (0 repair).
If you do some googling you will see there are two versions, and depending on the size/shape of SSD you are buying it may be better to buy one rather than the other.
If you do more googling, people have tried various drives and report on performance/compatibility etc but generally compatibility is good except with some samsung drives.
Same here (well, I have the "cheap" one without the Touch Bar). Everything has been replaced at least once (on Apple Care, fortunately) except the bottom plate.
> The only reason I got it is because the MacBook Air it replaced was dying
Same here. That MBA was a fine machine.