Yes the dexnav does indeed increase your chances of finding a shiny Pokemon. Every time you press search and encounter that Pokemon and KO it, it will add 1 to your chain. If you encounter over 40, your chances are raised to 0.5%. And once over 130 encounters, it will raise it to a massive 43.7% chance. Don't worry about the levels, those will not continue rising. After every 100 encounters, it reverts back to its default level, but the chance of a shiny says the same. I have found 9 shiny Pokemon by using this method. Also, its quite fun. Another thing. if you run, take too long to find the Pokemon, or scare it off, this will break your 'chain' and the chance of finding the shiny will be reset to the default as well. Happy Hunting!