This is the only part of your post i disagree with. i'm sure the club has put a lot of thought into these promotions, and, if run properly over a sustained length of time can have a fairly significant impact on the local fan base.
It's simple marketing really. Lose a few pounds on promoting these things, but even if the club gains an additional 100 regular supporters out of it, that could potentially be worth an extra £180,000 to the club over 5 years (based on an entry fee of £20 and 18 home games a season).
At the end of the day, for the club as a business, the cashflow is as important as it's perceived reputation in the town. Both are equally as important as each other.
With money being as it is, I'm sure MFC wouldn't go wasting money on these promotions without doing a bit of homework first.
That said, I think they could make a lot more of an impact if promoted effectively. Sometimes you have to speculate to accumulate.
That's why I think it's vitally important the club ensure that these letters are delivered as and when they should be. Given the fact that this is pretty much their only avenue of promotion (other than the 'fishel site) then it's just wasting the chance otherwise.