There is no downside to driving your engine around in that range. I regularly cruise mine along the highways at top gear at 2000-2500 rpm riding at the national speed limit. Sometimes I just let it lazily hum at 1000-1500 rpm when I'm just feeling "Old Town" and just want to let time go by. Once a while, when I feel like having fun, I let it rip up to 4-5k. Rarely above
The practice of revving your engine to "flush" it clean was originally for older engines: carbureted and early fuel injection engines where the fuel mixing process isn't as efficient as modern engines.
These early systems often would mix too much fuel or spray the fuel so far up the manifold that fuel would come into contact with its insides before effectively evaporating with the intake charge. These "wet" surfaces then become sticky mixing pots of particles, carbon dust, engine vapours and oil droplets that are being fed through the PCV and EGR systems. Depending on usage and the engine age, it would take years for the gunk to build up in the manifold and on the valves, but it would slowly reduce its airflow efficiency. Modern engines with their more accurate fuel injectors and direct injection won't have much of these problems unless the engine has clocked a lot mileage, has worn out piston rings and gaskets and is leaking lots of oil and vapor through the emission systems.
The other effect of "flushing" is forcing out the carbon build up in the exhaust system. Again, not a problem with modern engines which both give a more accurate fuel mix but also operate at much higher temperatures than older engines to reduce un-burnt carbon particles. And there is almost nothing in the exhaust system that would be affected badly by carbon build up.
But you should also take note that your mileage may vary. There can be special circumstances regarding your engine and emission systems. For example, my S62 engine has an emission control system where it pumps fresh air into the exhaust manifold. It's been reported that those air injectors would clog up with carbon after several years down the road and they recommend gunning the engine once a few weeks to try and keep them free of carbon. A little research online about your engine wouldn't hurt/
If anything, decent low RPMs guarantees less wear and stress on engines, and the occasional pedal to the metal still can help clean some internals, albeit not significantly much.
Then again, this is an ///M car, you can't deny that monster beneath the hood doesn't tempt you to hear it sing at 7000 rpm
