I had an '06 CC V6 SB before I traded it for my '13 CC V6 SB & the brakes on both of them, along with the turning radius, are the two biggest gripes I have about either truck. I say "gripes", but maybe that's to strong & would rather call the spongy brakes more of an 'annoyance' than anything else, especially if you aren't used to them. The brakes aren't to the point where I feel unsafe to drive the truck or if I were to haul anything. However, they certainly take a bit of extra work to bring the truck to a stop in a hurry & definitely take more leg work than most other vehicles I've driven over the years. In comparison, my father has an '02 Toyota Tacoma & the brakes on that thing will nearly throw you thru the windshield if you don't watch it. If the brakes on my Frontier were somewhere between my fathers truck & how they are now, I think they would be perfect. Come to think of it, I may have a partial solution to the problem.
There's a well known member on here who goes by the user-name X-Mods. Theres a part somewhere in his build thread that he was complaining about the spongy brakes of his truck as well. If I remember correctly, while he & one of his friends were working on his truck they noticed that when the brake pedal was applied the master cylinder had quite a bit of movement to it. So, he fabbed up a bracket that fits around the MC & mounted it to a factory bracket that's underneath the MC &, I think, part of the ABS brick. He said it seemed to firm up the pedal feel & also improved his braking performance. If anyone is interested, might look up his build thread & check it out.