ROS's are definitely my go-to tools. I started with a pad and then a belt sander but once I got my ROS, the others rarely get used.
I say that.. I used the 4x24 belt sander with 18 grit to "plane" some pieces of hard maple trim mostly into level, but still finished up with the ROS.
I'm no expert on inspecting used... I know most ROS companies sell replacement pads (replace from the mounting bolt down) which will let you convert between PSA and H&L but I don't know how to tell if one is worn out. Hopefully one more knowledgeable than I on this will jump in!
Check out that new high-tech cordless router.. wireless and no recharging required!!