I didnt preshade my AMT Falcon and had great results.

I inspired myself with a very interesting weathering tutorial series. Basically, it's a multi layered weathering technique using oils which results in a very realistic look; each step of the weathering collects a bit of paint in the recessed areas. You can also use the oils to create artificial shadows where needed.

Check it out:

Discoloration Tutorial Part 1 for Millenium Falcon Weathering

If ever you want to go that route, my only added recommandation would be to seal the kit with Future or your favorite type of sealer.

Cheers Jeita!