It's all about timing
I flew with Virgin to BNE and back (from SYD) last week.
On the way to BNE, a weekday (early) morning flight, the only joke I noticed was something along the lines of "It's certainly been your pleasure having us on board...". This was so subtle I don't think anyone actually got it. I don't know whether the crew purposefully toned down the jokes because of the time of day/passenger profile/fatigue, etc.
On the way back, a Saturday afternoon flight, the Cabin Manager made a fair few jokes that were actually quite amusing. Apart from the same "your pleasure...us on board" joke (which again, no-one seemed to get), included in his repertoire was this genuinely funny joke...
"Cabin crew, please be seated and hold hands for take-off...[perfectly timed pause] Ahh, Cabin Crew X [the previously introduced ccm seated on the same jumpseat as the CM], that's not my hand!"
Maybe you had to be there, but his humour seemed to be appreciated by a large portion of people on board.
Basically, i think that jokes are appropriate depending on the types of passengers. Really, it should be up to the crew to decide whether (and what type of) jokes are appropriate for each particular flight. However, I can absolutely see how it could be very annoying to hear the same jokes repeatedly if you frequently flew DJ.
Maybe you could introduce a joke quota, with each Cabin Manager given a maximum number of jokes per service and each joke can only be used a certain number of times before it must be retired??? Joking, BTW. Boom-tish!