Would it do any good to sow vegetable seeds under cloches now?

Though the seeds may germinate, and the plants may put on some growth, the
short days we are getting (and will have for some time) will mean that plants
will be etiolated (leggy). The answer might be the addition of growing lights
and possible chemical treatment to restrict effects of etiolation. All in all
I don't think it's really worth while. If you really want to do something with
the soil, maybe you could do some hardwood cuttings of hardy plants ready to
pot up next year. Winter is a good time to take hardwood cuttings of many
plants.

Not sure this is the answer you really wanted, but I hope it helps just a
little.

Dave.