Greetings! I've got a '98 D1 and while crawling underneath this weekend noticed that the cans have some significant rust. They haven't rusted through, and they passed state inspection.

Short of waiting for holes to appear or it to fall of, are there any benefits to replacing it before?

 

Not really unless you need to save up for a replacement or are not sure which muffler you want to buy.
The outer skin of most mufflers get a lot of rust but are OK internally.