Plus, keep in mind that a lot of the materials you would use for such a dredge on Earth won't work on Venus, because the atmosphere will corrode them.
If you need 50km long dredge, then it is a viable project in future, just like now it is with space elevator. Apparently that type of dredge will be needed to extract materials from gas planets(and 50km might not be enough), so that dredge will have to be developed anyway.
The most logical solution to make habitable world would be to bombard Venus with comets and small planets. They all have enough materials to stabilize Venus atmosphere and teraform it and also calculated bombarding can cause Venus to change axis and rotation.
That would help both bleeding off heat and helping with maintaining over-pressure in the living quarters.
Corrosion resistance will be a challenge but not impossible, there are many plastics which will withstand sulfuric acid.
- Lando Venrissian
Even at that altitude the cloud layer is still very turbulent and very toxic, and no structure will be absolutely gas-tight. And if the temperature is 75 °C outside, it's going to take insane amounts of energy to keep the inside of your hab cool - especially if it's made of metal and not rock. (A thin skin obviously isn't going to work.)
You can't mine Venus, and you can't explore the surface. All you can do is drift over the cloud layer.
So there's no point - except maybe niche tourism, niche planetary science, and possibly niche super-weapons research.
And after all that, you still have the problem of moving mass to/from your colony. 30-odd miles gives you a bit of an energy boost, but getting out the gravity well still isn't cheap or easy.