What do you expect to find? Interesting quirks of geology? The past presence of water? What? What conceiveable information might we be able to glean?
Mars is barren, with barely any atmosphere. We have no reason to believe there's anything there we can use, and even if there is, it would have to be extraordinarily valuable to compensate for the insane costs of extracting it and returning it to earth.
Putting a pound of material into orbit currently costs about $10,000. Most of the cost and weight of rockets is in fuel. It takes a mountain of explosives to launch a small capsule into orbit. It isn't sustainable. It isn't rational. Only the very select elite of humanity will ever leave this planet in anything like the foreseeable future, and when they do they have nowhere to go except lifeless wastes of rock, with death lurking at every point of failure.
We might theoretically colonize the moon, or Mars - but for what? Mining? They'd better have cores of Phlobitnum and Unobtainium, because otherwise it can never be economically sound. Terraforming? By the time we become able alter the entirety of a planet's enivornment, we'll have solved all our earthbound troubles, probably with help from the same developments that went into making terraforming possible. Farming? Sure, if we miraculously develop teleportation, because there's no way you can afford the fuel and materials to ship it between worlds.
Why? Why spend all this time, effort, money and resources? What possible justification can you offer? Scientific inquiry, knowledge for the sake of knowledge alone is not enough while people are starving every day.
So what concrete, realistic benefit can you name for us to gain from going offworld before fixing the mess we already have down here?