Why do people feel the need to make changes to a solution presented by another person?
This sounds to me very much (but not exactly) like a phenomenon Dan Ariely has done some research on, which he terms 'the IKEA effect'.
Of course, he will describe it better than me, specifically in Norton and Ariely (2012), Ariely et al (2008), and this TED talk.

Basically, what he's found is that people value things (furniture, lego models, plans) more when they themselves have contributed their own labour in creating them.

In Ariely et al (2008), they found that:


People are more willing to do dull, monotonous paperwork for less money if their name goes on the top of the sheet, and less willing if the paper was shredded after they had finished.
The same effect is found if you pay people to put together Lego models: people do more for less money if you don't take apart the models afterwards.


Norton and Ariely (2012) took a different approach, but showed largely the same thing:


People believe that the IKEA furniture which they themselves assembled was worth more than anyone else's furniture (measured by how much they would pay to keep it)
The same effect was found for origami animals.
..and for Lego models, but not if you take the model apart after you build it (because it's no longer the thing which you created).
...and not getting to finish assembling the furniture reduces this bias.


Hopefully, the link between this research and your question should be clear: by making changes to a solution, that solution becomes in some way 'ours', and because of that, we overestimate it's intrinsic value.



References

Michael I. Norton, Dan Ariely, and Daniel Mochon (2012), “The IKEA effect: When labor leads to love.” Journal of Consumer Psychology. Vol. 22: 453-460.

Dan Ariely, Emir Kamenica and Drazen Prelec (2008), “Man’s Search for Meaning: The Case of Legos.” Journal of Economic Behavior and Organization. Vol. 67: 671-677.