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.
I go to the stadium a lot less now (too).
"too" would not be used with this sentence by itself. There would need to be a previous phrase, for example:
I go to the city a lot less now, and I go to the stadium a lot less now too.
Now if we substitute the meaning you asked about:
I go to the city a lot less now. Now also, I go to the stadium very rarely.
Basically it is OK, but "a lot less" means "a lot less than before". It could have been 200 days/year before and now it is 50 days/year.
However, "very rarely" is "hardly at all", and should be a very small number in any case.
Best Answer
How much water a boat draws is a measure of the depth of water required to float it: a rowboat ‘draws’ only a few inches, a fully loaded flat-bottomed barge may ‘draw’ eight or ten feet, an ocean-going vessel with a very deep keel may ‘draw’fifty feet.
Figuratively speaking, how much ‘water’ a man ‘draws’ is a measure of his presence and influence. Jackie Treehorn is a very important man in his community; Lebowski is a nobody.
Galactic Cowboy suggests that the idiom here is one of drawing water from a well or other source, and that in water-poor Southern California a man entitled to "draw a lot of water" is marked as particularly influential. He may well be right: one of the earliest instances I have found of the idiom is from a 1938 crime novel set in LA and written by a former LA policeman in 1938 - about ten years after the California Water Wars. One seamier sidelight of that episode was the profits supposed to have been realized by insiders who bought up land in the San Fernando Valley, knowing that LA would have to annex the district to secure rights to the water. However, I also find the idiom in a report of an air show in the Pacific Northwest in the same year.