Get it replaced or wait for the chance of your car bending in the middle. At the least it will flex and could eventually cause stress fractures.
Think thats a bit excessive, can't see it being substancial enough to cause that much of an issue, Especially as the boot floor & the rear subframe would be taking up a lot more of the torsional stresses.
I did say chance.
Take a flat piece of metal add a u shape in the middle, a wheel at each corner, and weight in the middle and its going to flex in the middle. More so than a flat piece of metal.
The cross member is a weighty bit of metal with enough bends in it to make it very strong. Its got to be there for a good reason.
As I said the front one is called "reinforcement for tunnel" I'm sure VW wouldn't put it there if it didn't have a valid purpose. Its not there for performance or comfort so it must be for safety.
Paul