I find the extra $20 to be worth it. You walk out of Customs and you are at your car in 60 seconds.
Yes, it's absolutely frivolous, but a.) the additional $20 is - what? - an extra 0.5% (or less) of your cruise fare; and b.) if you're about to embark on a long drive home, you probably just want to get in your car and get going ASAFP.