I think the problem is not related to homebrew/Fink/Macports because I have exactly the same experience in my test. I.e. synfig crashes when clicking on created circles.
So I think we have 2 conclusions:
1. The packaging approach generally works fine - reports here sar that people can start application on various versions of OSX (10.6.x and 10.7.x)
2. The crashing behavior of synfig is related to general synfig unstability on mac OSX. And is not related to proposed packaging method.
Though, the last statement requires confirmation from users, who have synfig installed purely with fink/macports/homebrew. If they have different experience (synfig works more stable for them) then my second statement is untrue and we have to digg further with packaging approach.
This is just a quick response on this, I have not tried your dmg file, however I have the latest synfig build running, I installed it from the source files and compiled it with the terminal, ( in other words, I did not install Synfig using "sudo port install synfigstudio" command).
I say this is just a quick response because I have not used Synfig a lot for a long time, but I started it up and made a small animation on it and I have no crash at all, it seems to be running ok and I don't have this "making a circle" crashes your talking about.
A quick question, did you make the dmg file using macport and the command:
sudo port mdmg synfigstudio?
That command is what I have tried a couple of times and I always end up with an installation file that behaves like you described it after installation on another machine.
Cheers / Ulrik