Pretty much, it seems. I guess that's what it comes down to - I'm fine with losing Shiancoe for the year, since we have 3 TEs who are better than him anyway. I think the possibility that one of Brady, Welker, Mankins, Wilfork, Gronk, Hernandez, Mayo, etc. goes down with an 8+ week injury, combined with their value to the team, is sufficient that I'd save it.
It would take an injury to a more important player, IMO -- a Spikes, Gregory, Vollmer, Dowling type -- to make this a more compelling question. For the fourth TE, it just seems like there's not much reward for the opportunity cost. I'm really surprised that Belichick seems to have basically wasted this asset; he's the last coach that I'd expect that from. Either that or he holds Shiancoe in much higher esteem than all of us seem to.