For a single big ridge adding this sort of height will get you out of the turbulence. But the Grampians are the best wave soaring area in the UK, the UK height record was set there and is way over 20,000 ft - which gives you a pretty good marker on just how big a 'wave' can get.
On an average day if you see lenticular clouds in this area they typically start at 5000 and go on upwards. The turbulence on the leeside is usually not really apparent from above 50% of the height of the hills. So the advice from California pretty much 'fits'.
Crossing the ridgelines at 45 degrees is universal advice - but really only necessary if you're pushed for height or likely to encounter the leeside rotor.
The only real problem is that whilst you can usually get to these sort of heights on the east side of the Grampians the prevailing SW airflow often means the windward side has a lot of low cloud forming on it. So descending to a west coast destination will mean searching for a hole or going a fair bit further west to the coast.