When the mayor tells Rango that "people need something to believe in", he wasn't referring to Rango's heroism, but to his plot to use the townspeople's belief in Rango as a distraction to continue his plans.
Of course Rango is going to be capable of playing those blistering flamenco runs on the guitar. What else is he going to do with his time? Truly an artist in all facets, amirite?
This one is in a Viewers Are Geniuses sort of way. However it might be a bit of a stretch, some scientists think that humans got the notion of dragons from our brains fusing our mental image of the main predators together at an earlier point in our evolution. Which mostly consist of Snakes, birds of prey and cats. On the size scale that our heroes are on, snakes and hawks seem like dragons to them and, for the most part, that's how they act.
The Spirit of the West is more like the Spirit of the Western.
After Rango meets The Spirit of the West, Roadkill mentions that "we see what we need to see" in reference to the spirit. Rango needed to be a tough guy, so who better to take advice on playing a tough guy in a western setting than Clint Eastwood?!.
Not to mention the logic of one actor finding wisdom from another.
Much like the Spirit of the West himself, Rango is also a "Man with no name".
Notice how Rango broke a fine bottle of water which was probably worth more than he was. Notice the mayor not noticing? This could either be interpreted as Played for Laughs or the Mayor just didn't care, given that he was hoarding the vast majority of Dirt's water supply.
In the very first scene with Rango and the mayor's conversation, the mayor says that he's lived long enough to remember a time where the Mojave desert had flowing water. This answers a question not particularly raised: Why are there so many mammals and other animals not indigenous to a desert environment living in it? Because long ago they did at one point have an environment suited for them, until eventually the water flow was directed elsewhere and the place dried up.
Not to mention the mayor is a turtle, and they can live up to 100 years, so his words hold some merit.
Rango is a chameleon, as well as an actor. What better vocation for him than someone who can blend into their new surroundings?
Horned toads are known to defend themselves by squirting blood from pouches near their eyes. Waffles has red irises. These two things most probably do not relate biologically in any way, but the latter is a possible reference to the first one.
When Beans asks Rango what his name is on the way back to town, he goes on and on about 'his stage name, pen name, avatar,' etc., and is still going on listing all the different types of names he supposedly has by the time they get there. This makes sense when you remember that, at that point, he has no name, and when faced with a weakness or point of discomfort, what does he do? He brags and blusters and goes on at length trying to build himself up with talk.
"All we got here is cactus juice."- Qualifies as Getting Crap Past the Radar since kids are likely familiar with stories of Indians getting water from cacti, but a bar might be more interested in peyote than ordinary juices.
I figured it was more likely to be a reference to tequila than peyote, as a bar would much prefer to serve that.
During the extended ending, Rango explains that he has gun lotion in his bag, much like another cosmetics product related to guns: gun powder.
Right up until the Mayor calls him in to deal with Rango, Jake has been built up as this great hero-killer - "never leaves without taking a bloomin' soul." In that confrontation, he does by exposing Rango's lies and forcing him to prove his 'one bullet' story, essentially killing the larger-than-life persona he'd built up at the start of the movie. Rango even drops the sheriff badge in the graveyard, and gets it back once he realizes that he still is a hero.
On Wounded Bird's changing English skills: When we first meet him, he speaks in broken English. But throughout the movie it gets progressively better. That isn't a Plot Hole. You could argue that the broken English is deliberate.
We're probably better off not knowing what Rattlesnake Jake has in store for the Mayor in the end. The guy is pretty much described as a hellspawn Grim Reaper. Even if half of that is just myth, he clearly has far worse in store than just killing him off and being done with it.
And when you consider the various types of threats the citizens of Dirt regularly make to each other, trying to imagine the Mayor's fate becomes either hilarious or horrifying.