I have an old GS3, which is now running like a dog with no legs, that was really a toaster all along.
That said, I still want to use it, and I know it'll speed up a bit with a fresh install. The only problem is I need to keep a fair bit of the text messages (I organise a lot of things, and use them for notes).
There's probably a bunch of tutorials on this, but it's honestly been way too long since I've tinkered with this stuff, so I'm more asking about what kind of problems other people have had with it, tips, tricks, and if you know any good tutorials with enough detail to be useful if/when something stuffs up.
The S3 I used to own was okay with bare to no use with my own auto-levels of brightness, without anything but Google+ and youtube... To say the least.
The main problem I had with it, and it still persists, well because there's no active cooling on any phone (And since it's plastic): Temperature. It kept above 50 when on use, 45-40 (around 30s if lucky) when idle.
Then there's the RAM. I could've used swap on it to "increase" the RAM, but... Killing the longevity of SD cards.... No. It's the main reason why Samsung never updated it to 4.4 (The international version I own, at least.).
XDA Developers have a lot of this stuff covered.
Text messages could be backed up with hangouts I believe?