In the past, I used to buy toys in a pair. I would take one out for display and keep the other in MISB. Strangely, both my 1/60 VF1A Hikaru Ichijo DYRL version were affected by yellowing. If you see the pics on the battroid, you will see the yellowing were mainly on the wings, thighs and wheel covers on legs.
I am thinking of using white Gundam marker to conceal the the yellowing parts. Somehow I always procrastinate.
Here's a Yamato commercial ad on 1/60 Macross toys