1)
What is the significance of a curse in the Rasha's house?
1.
Malbim: Even if you see that the Rasha has a fixed house, know that Hashem's curse will take effect on it to vex him, make him lack and make him perish.
2)
Why does it say "u'Nve Tzadikim Yevarech"?
1.
Malbim: Even if the Tzadik does not have a fixed house, only Naveh, which hints to "Neve Tzon" (Yeshayah 65:10) and a temporary tent, also their Naveh, Hashem will bless it.