The original post read to me as someone wanting to be sure that the letter was well writte to convince the city to approve an exception to their regulations, and was therefore asking folks to read and comment to that any phrasing or points that might be detrimental could be modifed, removed or rephrased so as to present the strongest case in a positive manner.
Therefore comments about specific phrasing is not mean-spirited but exactly what was requested. To sit back, read and privately think, "hmmm, that word might trigger some negative ideas," but then praise the letter, or simply wish good luck without expressing the concern is not helpful.
I often ask others to proof and edit my letters.