I think if you can find uses for either or both bags, there isn't a problem with having two. Think about your wine bags... what would be your reasoning of having one in a MAM and one in MAB? If you think there will be a noticeable difference, and you'd appreciate it, then there wouldn't be a problem with having both a wine MAB and a wine MAM.
If you're thinking that you'd like to have a RM MAM and MAB for no real specific reason, then maybe you should hold off on buying another wine bag. While they are different sizes and beautiful bags, think of different situations where you would use one over the other... or if you would switch off between them. If you can't really think of any or if you picture the other one just sitting around... hold off on getting the wine MAM.
I also find that sales are so tempting sometimes.. but you just have to step back and think, "Do I really want this bag? Will I really use it? Or is it just the sale that makes it seem so appealing?" -- I absolutely have those moments where I think I need/want a bag because it looks nice and it's on sale... but you don't want to spend money if you won't end up using it. :okay: Good luck!