Both versions (with or without there) are perfectly normal things to ask. But if it is included, only the precise context (i.e. - what was said previously, who you're talking to, etc.) can tell us whether there refers to the location of the party, or the event itself.
Suppose, for example, you're talking to some friends in a pub, and one of them says "This is a really crazy place! Last week, two girls stripped off and danced naked on the tables!" It would be perfectly valid for you to say "Yeah! I was there! That was quite a night!"
The reason you can validly use there in that context is because essentially it can be applied to any place/time/event that's not here and now. Even though at the time of speaking, you're actually in the same location where the strippers danced, you're in a very different situation (they're not doing it now).
Contriving the situation even more, suppose instead, those two girls walk in and repeat the feat. You could say "That was crazy! I was here when they did that last week, too!".
In both cases you could use the other preposition. The "rules" aren't that fixed, and it very much depends on what you're emphasising out of different/same place/time/event. Not that I've ever been in either of those hypothetical contexts, but if I was I'd probably use there and here the way I've written it.
My reasoning would be that in the first case, both the time and the event are very different to "here and now". But in the second case the only thing that's different is the time, plus you've less reason to wish to emphasise the "not here and now" aspect of what you're talking about.
As regards "Are you there in the city?", you certainly wouldn't use there if you yourself were in the city at the time. Nor would you normally use it unless "the city" had already come up in the conversation. That's because in the city obviously refers to a spatial location that's not "here" (effectively, in that place, as opposed to in this place). It doesn't make sense to refer to that place if we don't know what place you're talking about, and it's confusing to have to wait for the words in the city to find out, so we don't generally phrase it like that. But if you had already mentioned the city, using there would be perfectly normal.
The difference between them and them all is usually just a way of making it clear that the action applies to all of the elements within the collective noun or group, and not just to some (but not all) elements of the group, or the group noun itself.
For example:
When my friends came over for a party, I cut them all a piece of cake.
In this sentence, a piece of cake was cut for every member of the collection "my friends" - i.e. each of my friends was given a piece of cake.
If we had chosen "them" instead of "them all":
When my friends came over for a party, I cut them a piece of cake.
We leave ambiguous the possibility that I cut a single piece of cake to be shared by the whole collection (i.e. one piece shared between all of my friends).
Similarly,
When we went to the pond to see the ducks, we gave them all some bread
implies that the author gave bread to each of the ducks at the pond, contrasting with
When we went to the pond to see the ducks, we gave them some bread
where it is possible that the author only gave bread to the collection of ducks as a group, and that some of the ducks in the group may not have been given bread.
So in summary, them all tends to be used where the author wants to make it clear that the action applies to each member of the group, whereas them can also refer to the group as a whole without specifically referring to each member of the group.
Increasingly the use of "them all" is becoming deprecated in favour of "each of them". Consequently, if you're not sure, use this form:
When my friends came over for a party, I cut each of them a piece of cake.
Best Answer
The second expresses a sense of urgency lacking in the first.