Blue book average asking price is $5,315 (stock). It is going to vary considerably based on where you are, and the condition. Most farkles don't add much value, some reduce value. Ultimately, it is worth what someone will pay
$4500 seems reasonable to me for a 2008 (1gen and no ABS, typical mileage). Muffler replacement = $0. But a full exhaust system, like yours, is attractive and I think would add several hundred. To me, flies removed and power commander would reduce the value significantly (removing the added $ of the exhaust). So, back to $4500- $5000ish.