Trail/desert riding beneficial for motocross?

I've always done both, and I've always found moto helped me offroad and the offroad helped me in moto. More importantly, they are both a blast.

Moto helps in offroad and offroad will help in moto.

I think the best cross-training for moto and offroad (offroad especially), though, is Trials. The balance, clutch and throttle control will be a benefit across all types of dirt bike riding.

Having the ability to navigate non-groomed terrain can't be anything but good for your MX skills. Yep, it helps.

You could argue any seat time on two wheels is beneficial in one way or another

I liked a video story told by 2 old geezer riders who own a parts shop. They told a story of a youngster who had just bought a new bike and had 300 bucks left over. The youngster asked them what he could buy to make him even faster on that new bike, the response from them was " buy 300 bucks worth of gas, and when it runs out, you will be faster."

So yeah, trail riding will help in MX...as long as you continue to hit up mx tracks regularly.

The old timers always told me seat time was seat time.