Achdus, REGARDLESS of the cause, is a good thing. If it isn’t necessarily for a great cause, that does not take away from the fact that many Jews got together and did something that they all felt connected to, in a positive way. We have so little achdus, unfortunately, that we CANNOT be picky about what to get together for and what we can’t. Thinking that achdus is only worthwhile for something YOU feel is good defeats the whole point of achdus! Because then, you will only strive for it when it is something you happen to think is right, which is the OPPOSITE of what achdus is all about. Real achdus is getting together with people, regardless of your personal opinion.
Also, it is not for anyone to decide what manner of saying prayers is considered right or wrong. Only G-d knows who is sincere and who isn’t. And if someone feels closer to G-d through song and dance rather than to cry, then that is what he should be doing. If that isn’t how you feel selichos should be said, don’t do it that way. Don’t diminish the level of holiness that other people may have achieved in a way that they feel elevated with.