Huh?
Of course Calvinists believe that the preaching of the Gospel "will make a difference". We know that the result of the Gospel being preached is the conversion of some sinners and the hardening of others. We know that the preaching of the Gospel is the sowing of the seed that God uses to grow His church.
The one difference between Calvinists and non-Calvinists is this: Calvinists know that God saves as a result of the preaching of the Gospel. Non-Calvinists hope that people will make the decision to accept salvation as a result of the preaching of the Gospel. (As has been pointed out, this leads to differing methods of preaching the Gospel.)
You're painting with a mighty broad brush there in you description of the non-Calvinists. Wesleyan-Arminians also believe in the preaching of the Gospel. A point I made quite clear in my orignal post.
But again, here's the difference.
You believe that the preaching of the Gospel will be used to cause the "elect" to come. But if you don't preach you still believe the "elect" will come.
So while it might make a difference, it doesn't matter.
Yes, we believe the the gospel is the Power of God and our non-Calvinist friends believe that they must be really convincing and say just the right thing or entice them into saying a sinners prayer or something.