I kind of stole the /etc/nginx/sites-enabled from the apache way of doing things. You just create a symlink from /etc/nginx/sites-available or simply issue a "mv" command between the two to enable or disable sites. Good for maintenance and testing/swapping configs. I also host a few other domains so it helps keep things organized.
Varnish wasn't really put in place to reduce load. Nginx is already very low on cpu and memory. So, since I have all this extra memory laying around Varnish can keep all cached and static files directly in RAM which is great. So images, txt and other static files, html, gzip, etc are kept in RAM if someone has accessed them before. I have my own dedicated server so I can spin up VPS's with decent amounts of memory. I've dedicated 512MB of RAM just for varnish caching, will add more if I start getting more traffic.
It's also nice because it can load balance between two back ends. I could put Vanrish on it's on server and split my webs server into two app tiers and point varnish to both.