I think Thornton was a desperate attempt at trying to ignite something.
One of the major pitfalls Dubas has had was placing too much emphasis on chasing that "killer instinct" (which I would not be surprised came from Shanny, who seems to be making a lot of stupid mistakes as a President and would be better off butting out altogether) and settling for subpar players like Simmonds, Thornton, and Foligno to get it.
Like if I had to choose between Thornton and Perry, it would easily be Perry... because it was clear that Thornton had nothing left in the tank even in his last year in San Jose and Perry still had something left to offer. Between Simmonds and Perry? Well Simmonds was 3 years younger and I don't think it is necessarily a bad bet for him to rekindle things in his hometown on a good team (which he had not played on for a number of years before he arrived).
Although in general, our "kids" are now in their mid-20's. They should not need a Spezza or Thornton or Perry or Foligno to teach them the ropes or ignite their passion. If anything, they should be the ones handling those responsibilities now and the ones that people turn to. They have had Spezza in that locker room for 3 years. An idiot could figure out what passion and desire looks like by now. If we bring in a 38 year old, it is because we believe they have something to offer on the ice, like Gio. Otherwise, Dubas has accumulated at least 5 young players who have earned a legitimate look at an NHL spot this year. Those spots used to be occupied by guys who were near the end of their careers and, for the most part, had nothing left to offer. Now they should be occupied by guys who are either hungry to turn their careers around (Tierney, Sanford, Rask, etc.) or guys who are hungry to get their careers started (Anderson, Robertson, Steeves, Holmberg, Abruzzese, etc.). And that is how we will get the surplus value to push us over the top.