PROS to ditching the ECM:
More flexibilty with tuning,
Less wiring
Easier for those that think ECM's are too high tech. (Those old guys stuck in the 60's

)
No sensors to replace (oxygen, MAP, etc.)
CONS:
You need to find a Carb and distributor
You'll loose the torque convertor clutch lock up.
Slighty higher emissions
Slighty less drivability
Slighty lower fuel economy
I don't see the ECM as an impediment. I would keep it until you truely find it's holding you back. With a cheap scan tool, you can take advantage of all the sensor's for tuning. The Q-jet's secondaries aren't controlled buy the ECM, so you tune for WOT the old fashioned way and timing can still be adjusted either the initial or with a MSD box.
First mod - find a 4.1 Buick V6 and get the four barrel carb and intake. Second mod - better rear end gears.