Ah, I see what you're getting at. I don't agree with all of your points, though.
Firstl, Verdun isn't going to fall, because it won't be as easily threatened. If there isn't any pressure from the German left (2nd Army), Verdun won't be simply cut off by a move from the Marne. Besides, any move from the Marne is going to be a very attractive spot for a French counterattack.
Second, you can either have the German center follow up on its successes, or you can have the right keep "more right", but not both. We aren't talking about a couple of extra armies here. The German center is exhausted, and you'll need all of the Ersatz divisions you can get to keep momentum going past the Marne. Besides...it isn't really realistic for the Ersatz divisions to go to the extreme right to "do their own thing" until the Battle of the Marne has been fought and won or lost. That is the point of attack.
Third...I wonder if those divisions will even get there in time to have any effect on the battles of very early September. The German logistics through Belgium and northern France is extremely taxed at this point as it is.
A couple of factual errors that need to be corrected: the Ersatz divisions were historically sent to Rupprecht of Bavaria's 6th army and von Heeringen's 7th army, NOT the Crown Prince's 5th army. He did not need these to maintain his advance where he was smacking around Sarrail's 3rd army something fierce.
Also, historically the German center was kicking ass and taking names when the order was issued to fall back. The German 4th and 5th armies were incredulous that all their gains were being thrown away at the point of victory.
Furthermore, the use of the Ersatz divisions was not in their offensive power, which they had little of, but rather the fact that they could hold down forts undersiege while the more useful reserve and active corps are freed up for the front. Maubeuge (not Namur as I erroneously stated before) held up 2.5 divisions by itself, which could have been better used at the front with the 2nd army. Same holds true for von Besler's corps at Antwerp and the brigade of active infantry holding Brussels. All these jobs were supposed to be conducted by the Ersatz units, but these were instead used in Lorraine on the offensive. Here they would be used as intended to besiege forts and hold supply lines, not use up valuable rail lines by moving to the front. Instead they would relieve these units to rejoin their armies. Basically it would mean two extra corps and a division would be freed up to use during the Marne on the right wing.
This has important effects at the Marne. Even showing up late will have an effect, as the brigade from Brussels did when it helped blunt the French 6th army on September 9th as von Lepel's men attacked into the rear of the French. Add in an extra corps and thing change dramatically. Throw in another 3 divisions and the retreat halts on the Marne and the center can continue to advance, separating the French 3rd and 4th armies, while continuing to cut off and encircle the 3rd army by throwing it back on Verdun/crushing it between von Strantz's 5th corps and the rest of the 5th army.
I also don't mean that Verdun to fall immediately, but if the German line holds on the Somme, Verdun is cut off and WILL fall eventually. It may take months, but it will happen. In the meantime, French attention is focused on the center instead of outflanking the German line in the West.
Also, the creation of a new 7th army at Brussels can begin sooner, which means that it can arrive where it is needed at a crucial junction, either between the 1st and 2nd armies, or on their right.