AFAIK the source code of the previous versions of Torque (TGE, TGEA) is said to be a mess. At least this seems to be a common point of criticism in the reviews on devmaster.net. I dont know though whether this is still the case for Torque 3D as there are no T3D reviews on devmaster.net.
The C4 engine is probably a much better choice in this regard, even if its more expensive.

Well i agree caus i've seen some Torque 3D C++ maths for additionnal collisions similar to the community tool HitBox Editor made by Superku ; and really i didn't understand
a lot it was realluy too complicated with need to modify several source code files
In comparison C4 engine code i've seen (C++) is lot lot more clear, and there is lot of explanation commentary in the code.

Even with source, i don't think it's the point that can make the difference to buy Torque 3D or not !

The strong points are the editors in the world editor indeed
that speed up your game making caus tools are already here
you've not have to code them !

Decal Editor

But for power and fuildity they should make a real playable level instead of pure graphic and simple 3D room !
I remember a demo they made with shaders, it was fluid but the PC was a rel big monster to make it run fluid !

But well to make little games it can be OK i think ,
you have just to test games like :
-Penny Arcade Adventures
-Hinterland

If you target small game or game partitionned in levels
it can be good perhaps ?