It's certainly worth it to get a bike that fits you properly regardless of what particular model that happens to be.
As to whether the additional features of the 7.5 are worth it - only you can answer the question of whether it is worth it to you. Obviously, the premiums are generally worth it to those who chose uplevel models, and not worth it to those who didn't. Trek offers no shortage of options in the FX line - you can find the value equation that best works for you. My personal "sweet spots" at different price levels are the 7.2, 7.4, 7.7.