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Yes.  I worked through your second patch and fixed a 
couple of minor errors (old_sz was declared or set).
Then, I tested and timed it.

The code had enough complexity that it took over an hour 
to prove that it worked and had no other hidden bugs.  
That presents a bit of a maitainability issue.

My abbreviated approach solved the quadratic time 
problem but does consume a memory multiple beyond 
your version.  

Ordinarily, that isn't an issue were worry about, but I 
presume that the reason someone is using the array 
module is that they have space constraints.  This string 
representation itself is going to be much larger than the 
array object (a four byte long, takes ten digits plus a space 
and a comma).  The question is whether there is a use 
case for repr() instead of tofile() or tostring() in a situation 
where there is just enough memory for the array object 
and it's string representation but not enough for an 
intermediate list object.

If you think it is critical, we can apply the fixed-up version 
of your patch.  But think carefully about whether it is 
worth the code complexity, maintainability challenges, 
increased coupling, and the duplication of list.repr code.