In many companies, the letter-opener is not the decision-maker, and obvious ads are trashed.
Instead of opening with big promises and assuming that you know the client's problems, you should open with specifics of what you do, and what you can provide (you put this at paragraph 6/7). And to get past the gatekeeper, add in an offer for something free. What that free thing is doesn't really matter, as long as it provides some business value and forces the letter in front of a decision-maker.
An additional tactic that I'm now testing out, with surprising success, is to say "I will be in [town] for a few days on [~2 weeks from sending the letter], maybe we could meet for lunch at [restaurant]". The soft-scheduling proves that it's not a mass-mailed letter, and it gives them a relatively short deadline to make up their mind about a meeting. I've only had one taker for the meal, but plenty of others scheduled in-office meetings for a more convenient time of the day, when they almost certainly would have otherwise opted for phone calls or emails.