Just YSK, vlan is not a security measure. It enumerates Ethernet packages with a number different than zero, and you can see all vlans if the network card decides it. So if some other device on your net is compromised, there is a chance traffic to your vulnerable box can be too. ( it gets a little more complicated with vlan aware switches in the middle. But not impossible)

Edit: BTW I feel you I too have a bit of older hardware thats on their own net where I just hope nothing bad happens til I come around to replacing it…