higher price premium for the 13" retina is mostly in the screen. for what it cost for the base model you are not getting a lot in term of performance and productivity quality, and that fancy retina screen will get old very fast. but if you bump the cpu up a bit and bump the storage capacity up a bit then you have the cost of the base 15" retina that just simply outperform the 13" in in every way, except portability.
however, on the other hand

, if you're spending someone else's money, then by all mean get the maxed out 13" in retina, though its still a cripple computer compare to its bigger brother, but hey, it ain't your money any way.
there are many enthusiast on this forum, and right now most are disappointed in what it has to offer rather than about what they are willing to pay.