Thank you for the input. I'm new here, and would like to put your ideas into some context re your experience level. Are you really good with networks, or more of a 'just try to get the thing to work' level techie like I am (with networks).
Part of my perspective was formulated at a time when I was using smoothwall as my firewall. That's a bare bones linux distro that acts as a dedicated firewall on any old pc. It turned out to be too complicated for me to get working well so I reverted to units like the DGL 4500 or the linksys units that are out there. But those guys are really into network security and according to the view they hold, the subnet isolation is a key component. If you're 'wise' in the ways of networks, and you feel that the subnet isolation is not all that useful in the case I've described...that's good to know. I don't need extra complexity!
The reason it came up is that I have no been able to get the DGL 4500 to work well on the LAN side. As noted in another thread I started, it does not seem to allow pcs on a LAN to connect on ports other than 80. So far my forum topic, a bunch of PMs to dlink employees that spend time here on the forums, and a long phone experience with dlink on the phone have moved me exactly zero inches closer to a solution. So I thought - buy a dedicated wired router and a separate wireless router, let them handle the diff tasks well, and maybe get some addtl isolation into the bargain.