I would take a look at the Assabet river in W. Concord and Stow. Wachusett can be very good in spring (you might run into a landlocked salmon or laker as a bonus). I have fished Walden since I was about 8 years old and most of the big bronzebacks that hung out near the railroad tracks are gone. Lot's of twinkies from what I've seen lately. Some fool illegally introduced carp back in the 80's and I think they have been feasting on the redds.
Most of the good water out this way has been privatized over the last 5 years including Ferrar pond in Lincoln (which contains some outright lunkers). Too bad a few irresponsible fisherman have ruined it for the rest of us
Best of luck,