[Direct Mail Strategy] Total Win? Or Miserable Idea?

If I were to attempt to quantify the "battle" we face with regard to converting prospects with direct mail, I'd express it in percentages like this:

25% - Opening the letter before it hits the trash
50% - Reading every word
25% - Calling you (every bit of this portion is tied to copywriting & a compelling CTA)

Background
I haven't tested this yet, but I think I've come up with a way to "win the battle" with the first two virtually every time, which is 75% of the goal.

No, it's not lumpy mail, although I do like lumpy mail.

And I read about some really creative tactics in another recent thread, like:

Tea Bag - "This'll take just 3 minutes to read. Sit back and have a cup of tea on me"
Sock - "Knock your socks off"
Dice - "Don't roll the dice with other companies"
Toy Soldier - "I go to war for my clients" (forgot where I heard about this one)
Condom - "You're gonna get screwed if you don't buy XYZ" (lol, kinda ballsy)
Dollar Bill - Not "lumpy", but a classic method pioneered by Gary Halbert (I believe)

But this idea I'm about to share is a little different because it dramatically raises anticipation of the letter itself. It's safe to assume they will be eagerly waiting to hear what you have to say (probably with bated breath).

Caveat
Your target must be HIGHLY targeted, because there's some cost associated with this.

Cost (per prospect)
$18.03 - Again, the letter will probably not get overlooked (and get read in its entirety), but at this price you'd better be supremely confident in the efficacy of the message when the letter arrives to them.

The Method
Mail a box of 500 business cards (drop-shipped and sent blindly - no receipt, no return address, no mention of the printer - just the box of cards). Each of the cards will be one-sided and simply say something like this (I haven't put much thought into the message on the cards - maybe you guys could help?):

"Bob,

This is worth repeating 499 more times:

I have an important message about your business. In a couple days you will be receiving a letter in the mail (hand-written envelope addressed to you).

Mike"

Discussion
Will Bob fear that someone has a vendetta, and that the letter will contain ricin or anthrax? LOL. Possibly. The copy on the cards should allay that fear as best as possible, while still maintaining a high level of suspense.

You'll notice I said "important message" and "about your business"... these phrases sound like marketing (which is ok - even preferable - in this case, I think). Also, the "hand-written" lets him know how to identify it so it's not missed.

Also, this is probably better suited for long-tail copy, which is what I am considering using it for.

Thoughts?