My guess is the main advantage is feasibility - a manned airship-like laboratory in the upper atmosphere of Venus is something we could likely accomplish sooner

My guess is the main advantage is feasibility - a manned airship-like laboratory in the upper atmosphere of Venus is something we could likely accomplish sooner than a manned mission to Mars, if we chose to make that a priority. Though the scientific benefit of such an effort would largely be secondary to other considerations. But that is fairly normal in the politics of human spaceflight.