Let's see what the history has been for up-and-coming QBs in NFL trades:
2011: Kevin Kolb gets traded for a 2nd round pick and a 3-year starting CB with one Pro Bowl appearance. Kolb was a 2nd round pick, 36th overall, with 7 career starts and 319 career pass attempts.
2009: Matt Cassel gets traded along with an aging starting linebacker for a 2nd round pick. Cassel was a 7th round pick, 230th overall, with 15 career starts and 555 career pass attempts.
2007: Matt Schaub gets traded for a 2007 2nd and 2008 2nd, plus the teams swap 1st round picks. Schaub was drafted in the 3rd round, 90th overall, with 2 career starts and 161 career pass attempts.
2001: Matt Hasselbeck gets traded along with pick 1.17 and a 7th round pick for 1.10 and a 3rd round pick. Hasselbeck was drafted in the 6th round, 187th overall, with zero career starts and 29 career pass attempts.
1995: Mark Brunell gets traded for a 3rd and a 5th round pick. Brunell was drafted in the 5th round, 118th overall the previous year, with zero starts and 27 career completions.
So did the Patriots, relatively speaking, not get enough in return for Cassel? Perhaps; then again I think Kolb and Schaub were still held in higher esteem by other teams because of how they were rated coming out of college. With so little pro experience to go on, teams still relied on the college film.