So I think I can bring this to a close. Sorry Tealvince.
I have been trying to use a very similar setup to my picture. I was able to block off the connection to the acetone and draw a vacuum of 23inHg. Then remove the block to let the acetone boil and the vapor in to the model chamber. The pressure dropped to 20inHg as expected
Leaving it for half an hour, just to see if it did anything showed no change. I didn't expect to see much as the acetone is still in the vapor.
Releasing the vacuum of the container so the vapor would condense gave very little signs of condensation on the glass. Whether this is due to the glass now having a residue of some sort on it to prevent condensation or that it was a room temp I can't be sure, but I then sealed the chamber again so any vapor could not escape.
Left it for another half hour.
I then removed the model from the chamber and was quite surprise how much you could smell the acetone, (not helped by having to lift the container off so the vapor flowed out, instead of lifting the model out) but even so there was clearly very little vapor.
The model was very slightly damp, and you could tell the surface was just softening, so I left it another half hour to see if anything progressed and to make sure it was dry.
After all that there is very little change. Even the top and bottom which were already pretty good still showed the print lines clearly.
I can see that something has happened but nothing close to being what you would say was a smooth model
I think this is down to the amount of vapor you get from "just" boiling the acetone. As it keeps reaching its pressure/vapor equilibrium it is hard to get much more vapor to then land on the model.
The only analogy I can think of is when a kettle boils. The instant water starts to boil there is hardly any steam, but leave it a little while and you end up with significantly more. There is no way to keep boiling the acetone as this would need you to keep pulling the vacuum, which then pulls out most of the vapor you have just created in the first place so it becomes impossible to get more vapor.
All of which brings me to say, that was all fun, but something that I can't see catching on as a smoothing solution.