My Android phone is rather old. It's running stock Android 4.1.2, which includes known security vulnerabilities. Unfortunately, this is the latest firmware which T-Mobile offers for this phone. Still, I'm fairly happy with Android 4.1.2.
I plan to upgrade to a newer phone in the future. Maybe a BlackBerry Priv, in a year or so, once the price of a used Priv falls has fallen some more. But not yet.
I generally only install apps from the Google Play store or from F-Droid; normally not from other sources. I surf the Internet a fair bit, normally using either Google Chrome or Firefox. I'm not picky about making sure that I watch videos hosted only on trusted websites such as YouTube; I'm willing to watch online videos hosted anywhere. I install app updates from the Google Play store perhaps once a month or so.
I don't have a data plan; I use Wi-Fi sometimes. I do download and view MMS messages from friends. I never receive MMSes from strangers.
My device is rooted. I use SuperSU to let me decide which apps can become root. I only let an app become root if I have a good reason to do so.
I see at xda-developers.com that there are various third-party "ROMs" (unofficial firmware images) available for my device, including CyanogenMod and others. If I install one of these ROMs, I can end up with a newer Android version, including all of its security fixes.
I already have ClockworkMod Recovery installed, which is a tool which helps to install third-party ROMs. I have a current backup of my existing stock ROM; the backup is stored on a MicroSD card.
Like I said, I am running Android 4.1.2, and it does include known security vulnerabilities. But I'm not a security professional and don't really know how bad these vulnerabilities truly are.
I would rather not install a third-party ROM. This would require time and effort.
Is it important for me to install a newer ROM? If so, how important is it?