Upgrading from Touring to Grand Touring costs $15K, and the benefits are 33% increased range and 48% more horsepower.
For me, the horsepower would be nearly meaningless, but I really appreciate the greater range. Not just because of the increased distance between charges, but also because you can charge to a reasonable range much faster.* And as the battery degrades over its lifetime, the smaller pack would become increasingly inconvenient. I'm glad I got a GT.
I haven't finished the breaking in period yet (I'm at about 1450 miles), but right now a fully charged pack would take me about 330 miles at highway speeds. Assuming this ends up around 340 once the breaking in period is done, switching to a Touring would mean my max range would be about 270. In my Model S, my real max was about 230, and there were many occasions when I was white knuckling to the next charger.
* I assume charging speeds are similar between the two battery packs, but you'd approach the top end of a smaller battery much sooner. I see charging speed begin to taper off around 50% SoC.