For your information, R class isn't a minvan and i seriously doubt minivan buyers can even afford or willing to pay for an R class.
No offence to anyone but seriously do you think a car that cost 60k+ and with options that can hover around 80k+ is targed to a minivan buyer?
and yes alot of incentives are out there right now, but it won't be reduced low enough to a point where anyone can buy it cause if that were the case, they would stop make it all together.
I own an R500 and had E550 for short period of time and i can tell you this much, It's a mercedes nonetheless meanign R class rides similar as an E class, just higher postion and not something you compare to Mazda,honda or toyota.
If you must compare R class to something, the closest one would be landrover,cadillac or even Gx/LX
In the end, It really comes down to ones preference in style and size.