It isn't really surprising. Latino voters already thought that the GOP was against them and illegals before Arizona passed this law, so why would it make a huge difference in how Latinos perceive the GOP?
No, it actually signifies something rather important. As was previously noted here, Reagan passing Amnesty in 1986 did almost nothing for the GOP among Hispanic voters (Bush Sr. won only about 27% in 88), despite the fact that they supported it. Now, passing a tough-on-illegals bill has also done next-to-nothing (at least for now anyway).
I think this means that what's dragging the GOP's share among Hispanics down is not the tangible immigration policies that they produce, but rather the perception that they don't care and/or are racist.
I don't think there's much actual opposition to securing the borders among Hispanics, i just think the Democrats have been successful in turning the immigration question from secure/open borders to support/hate Hispanics, in the same way they portrayed tough-on-crime policies in LA and NYC as being Anti-black.