Because no System 6 browser exists (I'm treating Samba as more of a stunt), the issue isn't really whether the putative NewBrowser would be worth using regularly. Rather than comparing it to modern browsers that operate on much more capable machines, we're comparing it to...nothing. And compared to nothing, something is pretty damn nice. It would be helpful to be able to download System 6 software on a System 6 Mac. Among others, it would permit us to bypass the "How do I get software onto an 800K floppy?" problem that often crops up when using a more modern computer.
And there's also the "we want to do it because we think we can" geektosterone spirit that ultimately motivates many of us here.