A more sophisticated look considers not just the ratio of salary cap from one year to another, but rather the trend in growth over a 2 or 3 year period. Take a look at the following graph:
Teams still don't love to shell out huge FA contracts, because the expensive FA contracts take cash out of the team coffers for signing bonuses. But when you're desperate like the Giants were this year, spending the money to get good players is an investment. When the team wins, the value of the franchise is increased. More on salary cap management in later posts.