This thread really should be on the Transportation Board, where those of us who fly frequently would be more likely to see your letter and be able to advise you. However, be warned that if it does migrate over there, you are likely to get advice that will not make you feel particularly good. We like to face facts over there, and your facts are kind of unfortunate.
I have to tell you an ugly truth of the airline industry: planes are normally NOT cleaned between flights on the same day. To do that would adversely affect turn time, and no airline on earth can afford to be that wasteful. They will be spot-cleaned if there are bodily fluids to clean up or if a seat is wet, but that's normally all that will be done until the overnight cleaning crew gets the plane.
The FA asked you what you wanted her to do about it because that is literally what she needed to know, and fast: what had to happen RIGHT THEN to make you able to take the flight? She asked the way that she did because she did not have any time to waste, and she needed to let you know that you would delay the flight if they did it.
Frankly I'm absolutely flabbergasted that they agreed to hold boarding in order to clean for you; whoever approved that literally put his or her job on the line, and may have been fired for it by now. Every minute that an airliner stands at the gate past scheduled departure time costs thousands of dollars; your described delay probably eliminated the company's entire profit on that flight. Normal procedure would have been to offer to re-book you on the first flight the following morning, in which case, they would not have charged you a change fee, but probably would not have given you vouchers for a hotel or food unless you really pressed hard for them.
I think your letter is focusing too much on the peanuts. Other than briefly mentioning the quantity of spilled peanuts as a reason for asking for a spot-cleaning for medical reasons, you should NOT dwell on the cleanliness issue. The state of the plane's cleanliness was normal, and the FA went out on a limb for you by even asking her higher-ups for the cleaning, so leave her out of it.
The ONLY legitimate complaint that you have is that you were verbally harassed by John Doe while waiting for the cleaning that Delta voluntarily provided. The man was understandably tense about how much that delay was costing and how much hell he was going to catch for it, but he went WAY over the line by making fun of you and commenting about your children, and THAT is what you need to focus on. You need to start the letter by saying that you wish to bring employee's John Does unprofessional behavior to the airline's attention, and then, you need to state EXACTLY what you want the airline to give you to compensate for the humiliation that you suffered in front of your children. You need to state the compensation that you seek in quantifiable terms: fare refunded, free flight voucher, 10K frequent-flyer miles for each of you -- whatever it is that will make you feel justice has been done. After that, you tell them exactly what he said to you. You don't have to tell them that you were understandably upset -- just quote him, and if he really said those things, it will be enough. (And for Pete's sake, leave out the line about the Communists!)
A long tale of woe that takes 8 paragraphs to get to the point will probably not even be read all the way through -- they will dump it and send you a standard form letter if they send you anything at all.
The fatal flaw that your original letter has is that it is only a vent. At no point do you tell them what compensation you want for the wrong that you feel has been done to you. It makes you feel better, but it is not constructive; it does not tell them what they as a company need to do to retain your business. (And don't expect them to promise never to serve peanuts again; they had already repeatedly stated their position on that.)
PS: I didn't check their website, but since someone has and mentioned the buffer zone rule, you should mention it in the letter; that you asked for the cleaning in accordance with their stated policy about creating a 6-row buffer zone. Also I second what Monkey said; tone down the "voice" of the letter -- it comes across tearful and whiney.