[TeMPOraL]

On Mars, gravity + thin air would likely limit the usefulness. But you're spot-on with Venus. Blimps would be great there. Hell, there were articles floating a couple of years ago suggesting you could park blimp on Venus above the corrosive layers of atmosphere, and conditions there could actually support a small base that would extract necessary resources from the atmosphere, and where humans would only need light shielding (+ breathing apparatus). I'm not saying building a cloud city on Venus is a good idea now, but I do think a long-duration mission to study the atmosphere would be, as data from Venus is also useful for studying climate change on Earth.