Even in our own solar system there are at least 3 planets that at one point in the past few billion years would have supported life, only Earth currently remains unscathed (yet). So there not being enough planets out there is a moot point really as we objectively know of at least a handful in our own solar system, with current observations (and future missions) outlining the strong possibility of some of them and various moons of the gas giants here may contain atmospheric life or sub-surface life on them today.
That's life as we know it of course.
This is why I like watching the Event Horizon and Cool Worlds Lab episodes, they speak from a strictly scientific standpoint and propose the possibilities using known science on what might be, and why it could still be, or may not be.
Like probes created by intelligent life billions of years ago that have only now reached our neck of the galaxy and some of these are what we may be seeing, which have then been reverse engineered by humans to some degree maybe, or black projects looking at exotic matter for propulsion - These projects have unlimited budgets and free roam to do whatever they please so have the luxury to create whatever under secrecy.
As Dr David Kipping has said a few times now in multiple episodes, we may well be the earliest emergence of intelligent life in the universe/galaxy, but because of the way the universe is expanding, finding other life like us gets exponentially harder as the lightyears of expansion take place, and once you reach a point in that expansion, you will never see even the light of galaxies beyond that point beyond the cosmic horizon as expansion has happened faster than the speed of light.
There are plenty of people who believe the reason we haven't discovered anything really fundamental in the past 100 years is because there isn't anything.
If that's the case, then we will probably never visit or be visited.
Quite a lot has been discovered though, most of it we can't explain, it was in the last 50 years that dark matter and dark energy became apparent as the effect they have on objects in the observed universe can be measured, just not the matter or energy itself as we don't have the technology yet to do so, but we know they exist.
In the standard lambda-CDM model of cosmology, the mass–energy content of the universe is 5% ordinary matter, 26.8% dark matter, and 68.2% a form of energy known as dark energy. Thus, dark matter constitutes 85% of the total mass, while dark energy and dark matter constitute 95% of the total mass–energy content.
We also discovered quantum entanglement from Einstein's theory of
Spooky action at a distance, where 2 entangled particles know each other's states regardless of how far apart they are. And then there's the discovery of particles that "change" when observed only (look up the double slit experiment) - Nobody knows how or why this happens, but there is clearly a fundamental fabric of the universe beyond our known dimensions holding things together and allowing some form of connection between everything.
So yeah there are some super crazy things left to discover and we will for many of them, we are just not advanced enough yet.