I think it is useful to consider why people applaude.
In the kind of cases you have mentioned, I think people are trying to show their appreciation, or their congratulations, to the person involved. This is not in itself a bad thing. As well, I think clapping is more common at other kinds of events, and to many, it seems the natural thing to do. So they are not trying to be disrespectful or inappropriate.
To some extent the priest has little control over this - if people decide to clap, what can he do? The only option would be to bring it up in a homily or announcement, or put it in a bulletin. One would have to be careful to be pastoral about it, since there is really no ill-intent.
But perhaps the issue is more this - why are some of these things that cause people to clap going on DURING the mass? I think sometimes the answer is - that is the only way the priest can be sure to get them in the church, which is another kind of problem. Ideally, announcements and new appointments should happen before the Mass or after, at which point applause would be ok. (It can be difficult to have them after if you are in one of those parishes where people leave before the end, and it can be annoying to those praying to have them at the beginning.) Could the missionary speak at coffee hour after? (But, would people come?)
I have no idea why people applauded at the end after the final song. That is the one that makes the least sense to me.
As an aside, a funny story from the High Anglican church I used to attend, where no one ever applauded during the Mass. One day there were some guest singers from the black Baptist church next door. They sang some lovely gospel stuff, and at the end, there was silence. Not what happens in their church. The priest nodded his head appreciatively and said to them, “they are applauding in their hearts!”
