When using cannons or turrets, do you receive range bonuses

Nope. ANY secondary weapon denies both the R1 red dice bonus and the R3 green dice bonus.

.....but you do get an extra evade dice if obscured by an obstacle.

Almost looks like you answered your own question.

But no, all secondaries ignore the standard bonus to attack or target's defense depending on range. Other things can still apply of course.

Nope. ANY secondary weapon denies both the R1 red dice bonus and the R3 green dice bonus.

OH and there's another rule we have completely missed! *mutters*, better go fix it in the next game....

Yep, primaries only for range bonuses.

Note that a "secondary weapon" is something that uses the "Attack:" header, such as Ion Cannon Turret, Heavy Laser Cannon, Proton Torpedoes, Homing Missiles, and "Hot Shot" Blaster.