My 2004 XP laptop is only used for tuning the tecGT engine management on my MR2. I turned off the wi fi so there is no security threat. My Win 8.1 tablet is used for everything else.
I have a couple of old 1999-2003! Compaq laptops I use for similar legacy app support -- an OBD-II interface, a 2m Walkie-talkie interface, and a handheld GPS interface. These machines have no personal information, heaven forbid no financial information, and although they connect to the world through my routers, I fail to see the threat. Other personal machines are Linux. If the OS were entirely lost I would restore it via an image backup. I do monitor and run AV on the XP machines occasionally but so far, nothing.