I agree with you floridagal; I don't think it's worth it to take your flight to pbi, and
I also think you've got the right idea to downgrade your card. You will still have zone 1 boarding and a free bag. The only things you won't have are 2 extra rdms and free economy comfort at the time of check in, but it sounds like you can do without those since you book in biz for long hauls anyway.