I too am a Geographer, am GIS Coordinator for a local municipality in Southern California, and ESRI is our city standard GIS software. I agree with everything you said about accuracy of USGS maps, and would add the accuracy of the elevation data is based on 30 meter digital elevation models, which introduce their own error. However I have found the accuracy of existing trails on USGS maps within TOPO to be pretty good for my area, SoCal and the Sierra. If you want to use the USGS topo maps for mapping newer (>1970s) roads and trails good luck. Most Topos for my area were created in the late 1920 and photo revised in the 1970s. luckily for my most of the trails I ride are 100 years old.