A space vehicle capable of spinning would create centrifugal force to simulate gravity. It might not be gravity equal to being on Earth but it could help reduce the effects of long-term weightlessness.

Humans don't belong in space, and they never did.

If you look at a manned space mission, 90+ percent of the resources are dedicated to keeping the humans alive. If we decide to go to Mars or farther, 99+ percent of the resources will be dedicated to keeping the humans alive:

Feeding them
Providing water for them.
Air for them to breathe.
Dealing with human waste.

If you stick with machines (computers and robots), all you need to do is provide them with electricity, and that can be achieved with a few solar panels.
We could have made much more scientific progress and learned more about our solar system if our entire space programs had been unmanned from the start.