"One day terrestrial ecosystems will be seen as subsets of much vaster solar-system or galaxy-wide ecosystems."

Yes, that's what I would expect to happen too. Just as people on this planet once had only a very local focus...like the Native on the island who thinks there are no other people out there beyond his island...the picture has kept broadening all through our cultural history. We've found myriad new forms of life on this planet which most people once knew nothing about. I expect we will also find myriad new forms of life in space once we become adept at traveling in space. It's all out there waiting for us. We just have to go and look.

Some of those forms of life will probably be more advanced than we are. If so, some of them have probably come here from time to time, both in the remote past and maybe right now.

How long they would stay or what they would do would depend on how much importance they place upon us. It may not be much.

We're also very dangerous people with all our weapons and our divided political paranoia. This would, I think, make alien lifeforms quite careful when and if they visited our planet. God knows, I'd be careful if I was an alien visiting here! ;-)