Or you could simply move a lot of that thick atmosphere over to Mars and have two more habitable planets...
Okay, now you're getting closer to my line of thinking. Y'see, once you get out into outer space, you don't want to clump up in just one place even out there.
It's nice to have other places to go!
So, yes, we'll want to get some of Venus' extra carbon dioxide over to Mars to thicken its atmosphere. Now anyone who "knows anything" about Mars will tell you the new gases will just leak away again, as if that's a reason to not do it.
So I say, "... and how long will that take?" And they actually don't know. Let me just say that from refurbishing Mars' atmosphere with gas from Venus and elsewhere, and occasionally topping it off from time to time, the pressure on Mars should suffice for some of us for the rest of the life of our species. No matter how you figure it, that's a long time, (sorta like the twelfth of never).
Of course, there is the matter of getting it moved. I don't object to beginning the process by building scads of nuclear-powered cargo ships, which use available volatiles as reaction gas. That is, the nuclear engine heats up the (say, dry ice) to really, really hot and spews it out as rocket exhaust. We could move a lot of stuff around the solar system that way, and we need to move a lot of stuff.
For example, let's say we're out there moving stuff and we spot a really big asteroid on a collision course with something important. Well, if we had a lot of ships with a lot of push, we could re-direct that asteroid into a more useful or at least safer path.
But eventually, we might want to start moving gas from Venus to Mars in a more "industrial" manner. We've already got plans for how to do that, already figured out and calculated like forty or fifty years ago, and just waiting for someone to get out there and do it!
My current plans call for humans to be out in the solar system in at least ten locations, making stuff, building stuff, and moving stuff, in the next few decades, all as part of a wide program to get US off this mudball before we suffer the same fate that "befell" the dinosaurs.