Hah, had I but returned a day earlier, Bromtaghon...
But seriously: lentro, I had a similar experience with the mission 6 part 2 where I whizzed through the lake after an update and never encountered a patrol, whilst before I was running into them all the time, so I suggested to Craig to increase back the chance of finiding a patrol (as I thought he changed the probabilities), and he said that the % stayed as usual. As for spin saw battles, I vividly remember checking that bit of programming working by having 100+ battles several times without a spin saw. On average, I get one after about 5-10 fights, but that's not always so. In any way, Spin Saw collecting is a plasuble method, but may take some time to get effective returns. By analyzing the average length of battle duration times one over chance of getting a spin saw you'll find the average duration for the average player before they can get the spin saw and cash that in (although the strenbth of the main is a big variable, I'd assume that this variable is comaparble across the Assassins, patrol and Tastidian battles). Then we can roughly compare which is the fastest method of acquiring gold and recommend it.
Personally, I've done all of the above-mentioned many times myself, and I usually go for spin saw as a variation to the routine, keep to the assassins early on and go to Tastidian later (as the Main becomes more powerful, it takes only a little longer to kill off Tastidian with thrice as much gold to gain).