As SEN, I've had quite solid upgrade experience when flying long haul to/from Asia.
PEK on LX was THE route to haul those OpUp's, with my quote being way above 50%. I didn't kept statistics on it, but (both directions) I must have gotten OpUps 3 out of 4 times in average. Made you feel disappointed when NOT getting an upgrade. I flew the route quite heavily (cheapest gateway to Asia, and then there were those times when LX "forgot" the fuel surcharge, making the flights literally free when counting in the miles..)
Other destinations were less frequent (or none at all), but I'd say I've been upgraded at least once on each route I would fly at least 3 or 4 times.
European routes, sometimes an OpUp (never expected, since I don't really check that much on short haul routes), especially on ZRH-Spain routes (and Spain-ZRH too) quite frequently.
Ex-FRA, China is also pretty good for upgrades. Good old times when Y to C was possible, it happened quite often. SIN, less so, but also a few times (only 1 or 2 on LX)
Ex-SIN, upgrade quote was surprisingly better than Ex-Hubs on that route.
TLV is another of my favorites. 4 out of 6 segments upgraded (all on LX) Y to C.
C to F is MUCH more rare than Y / Y+ to C, only one upgrade, ever (Funnily on a route they apparently seldom happen, GRU-ZRH)
Thanks OP to bring back some memories.. haven't been inside an aircraft in over a year..