MALC9990- I am a bit confused reading your post- are you saying you can use an Amex 2 for 1 voucher with miles? Is that just for a specific card, or does it work with any Plat. Amex card, which has the 2 for 1 offer for Business class tickets? I always thought the ticket had to be paid for full fare, and not "purchased" with miles.
My British Airway Amex Card (available in the UK only to UK based BAEC members) gives me a 2-4-1 voucher each year after spending £10,000 through the account. I use this for all CC spending until the £10,000 spend is reached. I then get a voucher which gives me 1 additional ticket when I redeem BA FF miles for a ticket. Thus a pair of tickets that might cost 400,000 miles actually only cost 200,000 miles.
The best way to use BA FF miles is for long haul premium seats in First or Biz class since there are still taxes and fuel surcharges to be paid and so Coach seats are a waste of the miles and the voucher.
So converting Marriott Reward points into BA FF miles by using the 5 day travel package and also directly into BA FF miles when BA makes an offer like to 25% extra miles offer makes sense since the 2-4-1 voucher doubles the value of the MR points.
BA also offers a 2-4-1 voucher in the USA for members who take out a Chase card which earns BA miles on spend however the required spend is I believe $30,000 in a year. It also has a big sign up bonus in miles.
So by leveraging the two loyalty programmes I am able to boost the value of the MR points significantly.
Things I NEVER DO with MR points.
1. Never use for nights stay unless a significant value is on offer. e.g. I have booked New Year's Eve at the Marriott County Hall in London. Cost for room in cash was over $1000 for one night so it was a reasonable 2.5 cents per point. Not as good as using the travel package but I only wanted the one night and it is a special night out in London for New Year celebrations.
2. Never Use for other purchases - a big waste of points.
3. Never use for cruises - again a major waste of points on something you can get quite easily for cash with price reductions.