Interesting questions which got me thinking. Here's what I came up with.
To keep it simple, suppose Bob and Tom both have dues of $1200 ($100/month)
Also, both have the full $1200 in the bank in a saving account that draws 3% interest. (That's 0.25% monthly)
On Jan 15th, Bob pays in full using his Credit Card and gets $12 Disney Reward dollars.
Tom has $100 deducted from his savings account.
Month 2, Bob's full $1200 sat in his account for a month and he gets $3 interest, so his total so far is $3 cash and $12 in reward dollars. He pays the credit card in full (if he doesn't he'd be paying high credit card interest rates which would totally negate any purpose in getting reward dollars)
Tom had $1100 in his account for the month and receives $2.75 in interest. He then pays another $100
Month 3. Bob's money is gone and gets no more interest for the remainder of the year. Tom's $1000 balance for the month got him another $2.50 in interest.
Month 4. Similar, Tom's savings balance for this month was $900 and he gets another $2.25 in interest.
Carry this all the way through the year, and at the end, Tom has received a total of $16.50 in interest compared to Bob's $3.00 in interest and $12.00 in reward credits.
The final kicker: Taxes. Bob pays income taxes on $3.00 while Tom pays on $16.50. So depending on your tax bracket, you are ahead one way or the other. A 25% tax bracket for example would mean Bob paid $0.75 in tax so his net result is $12.00 in rewards credits and $2.25 in interest, equals $14.25.
Tom pays $4.13 in tax, leaving a net result of $12.37, so in this particular scenario Bob got more out of it by $1.88
This is predicated on a saving account that pays only 3% interest. If the savings account paid 4% interest, then using the exact same numbers as above, and same tax rate, Tom wins by $1.50
Just crunching numbers for fun. This is pretty much a wash no matter which way you go. If someone has lots and lots of points, then in their case it may be worth it to do the calculations but I suspect someone with thousands of points is in more than a 25% tax bracket.