Put in more survey sensors. Even Improved or Advanced Geo/Grav surveys only provide few points per sensor. This is the most common issue with "self-guided" "fire & forget" surveys: due to small amount of survey points generated per hour, the ships spend far more time parked than moving. So double or even triple the amount of sensors and you'll see the fuel going down more in line with deployment time and maintenance supplies.
Unfortunately, the answer to your other question is "no good way". There are too many variables and not enough options to fully automate surveying of multiple systems. Thus, as others stated, it's generally best to optimise your survey efforts into doing one systems as efficiently and as automated as possible, leaving you to micro-manage what happens between systems.
It also helps to keep in mind that geosurvey and gravsurvey are somewhat different animals. The number of bodies, the number of points per body, and the distances involved can vary greatly from system to system. While the distances and points vary, there are always exactly 30 gravsurvey locations in a known configuration. Also, don't neglect surveying asteroids. They often have worthwhile mineral deposits, and comets are almost guaranteed to be worth mining.
In fairness, the only way to have enough options to cover every use case would be to support player-side scripting, and Steve is fully justified in NOPEing that.