Agreed. I'll usually test the lines with a few probing attacks, and exploit any opportunities that arise. I do keep myself from getting committed to the 'big one', unless the situation gets out of hand (French lines blown wide open, etc).
It really depends on if Beligium has gone Allied or not. If she is neutral I am usually content to just sit and bide my time until Spring. The reason being that there is usually no reason to expend units dismantling the Maginot Line...since you will have a clear shot through the Low Countries every time.
If Belgium turns toward the Allies, the French will move up - and necessitate pushing them back a bit to get good positioning for when the bonuses kick in.