Well, I'll complain that heuristics just don't seem to work. Or, at the least, I've not been exposed to a heuristics program that really works.
The rest of your post makes sense to me. Most AV's do indeed hog resources, sometimes to the point that a rational person wonders why he even bothers.
Common sense protections such as you mention are the first line of defense. The wife has gone back to Windows 7, after several years of Linux. She recently complained of some stupid thing or another, and during our conversation, I asked where she downloaded her software from. She DID NOT go to the developer's site to download directly in several instances. She mentioned CNET among other download sources. Geez, Louise! Where else did you download from? "I can't remember, I just did a Google search and downloaded stuff!"
I'm still on Linux. I almost never install anything that doesn't come directly from a Debian or a Sabayon repository. Can't trust anyone these days! Best practices are well worth observing - even though I'm the only user on this machine, I haven't given myself any administrative rights. When I want to do anything, I have to sudo the privileges - then I revoke those privileges immediately after I finish.
Compare that to Windows users who log on as "Owner" or "Administrator" routinely, LMAO. They are just begging to be owned!