I want to use my phone as a GPS, but I don't want to turn on high accuracy to assist Google's wardriving. What am I to do?
You can use the "Device only" location mode, found under Settings->Location->Mode. The key performance impact of this setting is in the time to first location fix. It can take minutes to find your location initially, but later updates will be quick.

I am not sure whether you also need to disable use of WiFi and Bluetooth for scanning purposes, but if you are concerned about privacy I would disable these:
Settings->Location->Scanning