From what I know..

1. As of now, still only non prepaid rates can be paid by vouchers..so yes, usually a big difference there.

2. No answer to this.. BUT I find this with many other top category hotels in other chains too.. for eg.. most if not all Holiday Inn Express's have bfast and internet included whereas many Crowne Plaza's and Interconti's dont..

3. Conversion rate is still the same as you mentioned and so yes, there is an arbitrage oppty still if you pay a Eur bill with USD vouchers.. BUT , IIRC the exchange rate is now that applied by the hotel and not what is declared by some agency..