Now we know they are desolate and pretty much lifeless.
Well, no, we dont really know this. There are still some spots in the solar system where life could exist, and Mars is still one of the contenders.
Its also not just about "finding" life. Its about not wiping it out if it does exist.
We could find interesting life on Mars, and then have our imported bacteria eat it like its candy.
Personally though, I dont think there is life beyond earth. And my reasoning stems from the Fermi paradox.
If life was easy to find, there would be aliens everywhere we look. We dont see them, so they are not there, so life does not form easily.
And colonising venus will be way harder than Mars
There could be lots of life beyond Earth, just maybe not intelligent life that could leave a mark for us to have seen. The universe is pretty big and despite all our accomplishments, we didn't really leave any signal that could be detected until about 60 years ago (earlier radio signals would have been drowned out by our atmosphere). So our existence is only broadcast to possible aliens in a 60 light year radius (and inverse square law probably fragments that)
Also, aliens may have been gallivanting around the galaxy (or other galaxies) millions of years ago. The odds that 2 civilizations in close proximity at similar levels of development is highly improbable and just a poofteenths chance away from impossible (though in an 'infinite' universe it has to exist somewhere). For all we know there was some form of intelligent life in our galactic backyard long ago but just like every civilisation, it fell
The universe also still has trillions of years where it can harbour life as we know it. For humanity to survive or at the very least leave a legacy, it should launch seeds of life in every direction and let 'panspermia' do the work.
For all we know we are the legacy of an alien race ourselves.
I dont think it matters that we have 'humans' live long into the future. If we can seed another world with the building blocks of life, and that world goes on to create life of its own, that's good enough for me
It doesn't matter if this life will never know of their origin and be able to thank us. Just the thought that humanity has a legacy of that scale that could last millions or billions of years past our use by date is awesome enough.