Your examples involve creatures that we already know about and have interacted with and "integrated" into our lives (one way or another).
But I suppose the counter-example is "it depends who finds us" -- if it's an intergalactic scientific exploration team of aliens, they'll probably be as nice as can be. If it's an intergalactic mining company, maybe not so much.
The equivalent here would be the contrast between a scientific expedition to explore new species in the Amazon Rainforest (i.e. people who would be benign and take an interest in new species) vs. a bulldozing crew out to find more land in those same rainforests ("Oh look, a bird. Ok boys chop down that tree").
As human as it is, most exploration has been grounded in financial and egotistical needs, not scientific exploration. Maybe the civilization is just as curious as we would be and thus would come for selfless reasons, but that's a pretty big assumption.
At galactic scale, there's not much difference between a Mars cockroach and a regular cockroach.
There's not much difference between one species and another here but we still study all of them in great detail.
Don't mistake your lack of intellectual curiosity about a certain subject as being a trait shared by everyone else. I don't care about football but that doesn't mean nobody else does.
Similarly, as I said already, if you're going to go cruising about the galaxy, you're going to put people on that ship who are interested in what they're going to find. Otherwise there's no point.
See my response to the other guy who brought up a similar analogy.
Society, as a whole, probably doesn't care about a new cockroach species. But there is someone who does, just on Earth.
Similarly, among any civ that has the basic biological impulses required to become an interstellar civ, there are going to be people who want to branch out on their own, who want to study something on their own, who want to be the first to contact something new. It's all those millions of edge-case members that will do the amazing stuff.
Actually, as far as our interactions with other life forms go, we either ignore them (intestinal bacteria), keep them away (diseases), exterminate them (pests), or harvest and devour them (farming), or kill them for sport (hunting). The utterly insignificant fraction that become objects of our affection are those that are extremely close to us on the evolutionary scale. This wouldn't be the case with a civilization advanced enough to visit. Not even close.
If someone somewhere discovered a new breed of cockroach, would you care?