People go entire lifetimes hoping for their team to win just one SB (or championship in whatever sport). Even if Brady leaves this offseason, it will have totally been worth it had the alternative been not winning last year, but having a new franchise QB in place for the next 10 years.
Of course, as Roy says, if we could have had both with Jimmy G sitting on the bench, then sure; but that just didn't seem plausible. That 6th SB meant everything and, frankly, means even more with Brady winning it just to add to his legendary status in NE.