In 14 years as SEN I receiced numerous shorthaul upgrades Y to C until about 2015. Since then, never.
On longhaul flights I got a couple ones from Y to C (LX JNB, LH SIN, ADD) and one on LX from C to F (HKG, service recovery). 2014-2017 I flew mainly SQ and was PPS (and SEN) but never received an opup. Since 2017 almost all of my longhauls are in First and on the rare occasions where I had a C ticket I was never upgraded despite being SEN in sometimes highest business fare (J) on ex ZRH tickets. There were always HON ahead of me on the grading list which is fine.
but for sure I get the impression that the more I flew and spent, the less they opuped me.