I see the preamble as just one part of the solver's route map to the solution. I have set themed puzzles without preambles, and puzzles where the preamble was integrated with the clues. The important thing in my view is that between them the grid, clues, preamble, title etc must provide sufficient information to enable the solver:
1. To progress through the puzzle without making mental leaps that could not reasonably be expected of them,
2. To know when they have crossed the finishing line, and
3. To identify unambiguously the intended solution.
Attempting to avoid ambiguity tends to result in wordy preambles, but puzzles such as the Listener have tight space constraints which mean that the preamble will often have to be pared down significantly. This should be borne in mind when solving: the editors will ensure that the key points are covered, but careful reading (and re-reading) may be required - the words used will all have been carefully chosen.
Regarding misdirection, there are rules for preambles, just as there are for clues, and these must not be breached in order to mislead. If a preamble were to use the standard text 'Each clue must have a letter removed prior to solving', I would not be happy if I found myself removing 'bee' or 'Rigsby'. I'd have no problem, though, with a preamble saying 'Six clues must have an element removed prior to solving' when 'tin', 'gold', 'lead' etc needed to be removed, as there has been no deception (the term 'element' having no standard meaning in a preamble).