Why does it specify their vines and fig-trees? The hail struck all trees?
Radak: Specifically they are mentioned also in Mizmor 78:47, 1 for they are the majority of trees in Egypt.
There is it says "Gafnam v'Shikmosam." Radak explains that Shikmosam are a kind of wild fig.
Why does it say "va'Yeshaber Etz Gevulam"?
Yated Ne'eman (5771 29, Musaf Shabbos p.5): Shemos Rabah 13:4] says that the locusts clarified the border of Egypt. Why was this necessary? The frogs already clarified the border (ibid., 10:2)! After Makas Tzfarde?a, they planted trees on the border. The hail broke all the trees, including those on the border, so they needed another clarification of the border.
