Neither Starr County nor Cameron County are good examples in reading the Texas Latino vote, especially in South Texas.
Cameron County, which includes Harlingen, has a large population of old-school DINO Germans and therefore makes it more conservative than surrounding areas.
Starr County doesn't have enough population to really warrant comparison to the larger Texas Latino population, but for example Bush 43 in 2004 ran almost 10% ahead of Bush 41 and Ross Perot combined there (Bush 43 in 2004 ran ahead of Reagan in 1984, not many counties in America where you'd find that.)
The best counties for general comparison are Hidalgo County, containing Brownsville and McAllen (Kerry 55%-Bush 45%) and Webb County, containing Laredo (Kerry 57%-Bush 43%). In both counties, Bush 43 ran roughly about 10% ahead of Bush 41 in 1988.
Overall, I would say that the South Texas Latino movement has been about 20% towards Republicans since the mid-1980s and somewhere in the range of 10-15% since the mid-1990s. This is starting from a base range of about 20-25% in the mid-1980s. Now, on the local level, the Republican party still basically does not exist in these areas, but it'll probably just take a strong Hispanic politician from this area at the statewide level to change that, just depends on when this happens (it might be 5 years or 25 years).
Urban movement has been smaller, but is still noticeable. My old CD-29 in Houston is a good example of this.
However, Texas Latinos really do not compare that much to Latinos in other states. Politically, they tend to be socially conservative and fiscally fairly liberal and support free trade, a combination which I don't necessarily believe you'll find anywhere else among Hispanics except southern New Mexico.
Moreover, the Census figures do not translate well into voter breakdowns, because the Census also counts non-citizens who can't vote. So, the drop-off in the Latino proportion of the vote is exponential to the drop-off in the Latino percentage of the population.
Whatever the case, here's how the top 20 Latino counties in the U.S. voted in the 1996 presidential election:
1 Starr County TX: 86.94% Clinton; 10.41% Dole
2 Maverick County TX: 80.58% Clinton; 15.94% Dole
3 Webb County TX: 76.67% Clinton; 19.02% Dole
4 Brooks County TX: 84.43% Clinton; 11.84% Dole
5 Zavala County TX: 82.32% Clinton; 14.50% Dole
6 Jim Hogg County TX: 79.30% Clinton; 16.94% Dole
7 Hidalgo County TX: 66.49% Clinton; 28.84% Dole
8 Duval County TX: 84.94% Clinton; 11.65% Dole
9 Zapata County TX: 72.90% Clinton; 21.27% Dole
10 Willacy County TX: 70.02% Clinton; 24.62% Dole
11 Cameron County TX: 61.76% Clinton; 32.63% Dole
12 Presidio County TX: 70.22% Clinton; 22.32% Dole
13 Dimmit County TX: 74.96% Clinton; 20.19% Dole
14 Santa Cruz County AZ: 64.17% Clinton; 27.62% Dole
15 El Paso County TX: 62.33% Clinton; 32.11% Dole
16 Mora County NM: 68.76% Clinton; 23.43% Dole
17 Guadalupe County NM: 69.59% Clinton; 25.12% Dole
18 La Salle County TX: 69.69% Clinton; 26.10% Dole
19 Val Verde County TX: 53.05% Clinton; 41.10% Dole
20 San Miguel County NM: 72.51% Clinton; 20.09% Dole
You'll likely dispute my use of 1996 instead of 2000 or 2004, but most of these are in Texas and GWB had a strong home-state effect. If it makes you feel better to go with 2004 though be my guest..