I'm sorry, Mike, but I can't help you on the DD-WRT front as I haven't used that firmware in a few years now. I'm running pfSense in a virtual machine with Ubiquiti & Cisco APs.
I wanted to get away from a platform-dependent setup with limited power and migrate into something that was easily upgradable and portable. A VM platform gives me that. One day I started to worry about my router failing and my lack of preparedness for when that happened -- considering how much was relying on my "non-standard" home network. Ironically... as I was making the transition it started to happen as the reboots and lockups were mounting. People balk at running a computer 24/7, but it basically runs my house and even with all the VMs I have running it uses less than 40w at idle -- it's an older i7 platform.
The benefits of using your own DNS servers really depend on your end goals. It could be because you want to get IPs from the root source, you want to protect your network from malware sites, you want to prevent users from accessing "bad stuff", or, as Pete pointed out, you want to get away from your ISP targeting you with ads.