““Kickstarting life” on a planet unsuitable for life seems like a fruitless quest to me...”
There are earthbound microbes and the like, which have evolved to live in environments even more hostile and extreme than that on Mars.
Scientists have dubbed them, ‘extremophiles’.
It’s been postulated that some strains could easily survive on Mars.
To sustain human life (which is what we're concerned about here, or nobody would be talking about Mars), we would need to grow actual edible food, not putz around with bacteria. Unless you've discovered an extremophile potato, they're not really relevant to the conversation are they?
I suppose if we could get bacteria to grow there they might begin changing the environment on Mars to make it more conducive to life, but they wouldn't give Mars a magnetic field, or move it's orbit closer to the Sun, and anything they could accomplish would be taking place on a geologic timescale, meaning it would still be irrelevant to us, and probably to all of our future descendants.