This guide will only deal with completing the Fast and Insane difficulties.
Others have commented that using builds focused on Boost or Protection has worked well for them. That wasn't the case for me, and here's why:
Only the last 10 seconds of the race matter. Throughout the rest of the race, you will be passed even at max boost with max top speed, and you will be hit no matter the shields you're using. It is even possible to use the Dog chief skill (boost & protection) and yet still be passed and hit. For these reasons, I found the following build to be extremely useful:
Chief: Ed & Bev Bighead
Crew: Really Really Big Man
Gary is the best Crew member, in my opinion, as he ensures that you'll get your Chief skill faster no matter what you're doing.
The Bigheads (Frogs) are necessary for the vital last 10 seconds of the race, and will single-handedly win you races. They pull back whoever is in front of you, and give you a boost to pass them. Use this skill throughout the race to make it go by faster, and then at the end of the last lap to ensure victory.
Really Really Big Man will boost you forward when your skill becomes available, in case you need that extra boost to use the Frogs on whoever is in 1st.
Basically just race normally, your competence literally does not matter, the race will proceed the same whether you're racing perfectly or purposely going slow. Then at the end, use your skills to overtake before the rubberbanding can screw you over again. And if you get Pig'd or Jellyfished at the end of the last lap of the last race, sorry, it happens to all of us.