The Zen of Spark
I maintain 13 airplanes for a flying club averaging 500 hours monthly. We have transitioned to Tempest plugs, having used Champions for 50 years. The reasons are exactly as you outlined. Center electrode cracking was getting annoyingly significant, but the real straw on the camel’s back was the resistance issue. Both have been completely solved by changing plug brands.
High resistance was showing up as hard starting, primarily on our 152 training fleet, and to a lesser degree on our Warrior fleet. We first noticed it several years ago on a newly overhauled engine with new Champion REM37BY plugs. Within 150 hours, it was almost impossible to start, although once it did start it ran just fine.
Troubleshooting eliminated all other engine and mag problems. When we finally changed out the plugs with new (Champions), it started instantly. Two hundred hours later, it was back to burning up the starter. At the time, I heard that Cirrus owners were having similar problems.