I think this is a personal values decision. By all accounts the R Series is very capable... and the percent improvement stepping up to the S Series is not necessarily equivalent to the monetary cost (as those of us who would be ecstatic with a set of Speakers costing
just the difference between those L/R Speakers alone might find value in).
We've had many a thread where the conversation has centered on the point of diminishing returns.
I'm not suggesting that there isn't some value to the S Series... let's face it, the reviews alone show there is a value to them...
*shrugs
Maybe it's not much help, but I think you really just have to have that honest conversation with yourself about whether you will be happy with just the Rs, or will you find yourself longing for the Ss... always wondering what if? And that's just not something I think anyone hear but you can answer.