Greetings, goodman Yames!
I will preface my comments by pointing out that our situation in Tarndale is an unusual one, to say the least. The exact boundaries of Andarean authority are still being fleshed out, so I will confine my description to the situation within the borders of Andar - which is where many of us spent a great deal of our adventuring lives.
For about half a decade, I served as Baron of Keystone Village. My duties during this time involved (in the main) ensuring that my people were safe and prosperous, as well as collecting taxes and enforcing the laws of the Kingdom of Andar. This is not a simple charter. I am happy to state that my Barony remained well-fed and provided food and supplies to other areas of the Kingdom during my tenure, but this required constant work and vigilance. My usual schedule involved seven days a week of ten to twelve hour days. The times I visited Westgate and Iron Falls were about the only times I had away from my duties - I do not know many non-nobles who would consider their time in those places as a "vacation". I would refer you to Kasuni and Sir Avaran as those who know my work well, if you have other questions about the amount of time, diligence, and sheer effort that is involved in managing and leading several thousand people.
This is the primary duty of most landed Andarean nobility - doing their best to keep their people secure and well provided for. Whether a landed Lady, a Baron, a Count, or a Duchess, the huge majority of their time and effort is spent thus. Some are more visible than others to the common folk or adventurers, but be sure that the mainstay of their lives is working on behalf of the people they rule over.
The duties of non-landed nobles are somewhat different. Pages, Squires, Knights, and unlanded Lords are to look out for Andar and its people in a more general sense, along with exact duties based on their particular assignment. Knights and Lords help enforce the laws of the Kingdom. Knights specifically are to seek out and punish those who would do ill upon Andar's people or lands. Pages and Squires are in training, and thus have very specific duties based on what they are learning.
I do not know that you appreciate the responsibilities inherent in enforcing the laws. Let us take Sir Avaran as an example. Perhaps we encounter a necromancer and Sir Avaran's duty is to sentence and execute the villian. While the efforts of all adventurers are appreciated in helping apprehend the foul chaos user, Sir Avaran will inevitably be the one after whom the creature sends its diseased minions if it resurrects. During my time in Andar, I had multiple assassination attempts upon my person by no less than Llantry's elite units - simply because I was a noble, assigned to protect the people and the land. Even in situations like this, though, our duty is served precisely by being targets for the enemies of Andar. We defend against the foes of the Kingdom so that they focus on the nobility instead of the commoners, a duty which is often not understood by those who have not been in this position.
Many people see the advantages of being a noble without understanding the responsibilities and penalties that come with it. True, there are nobles who misuse their positions - and justice eventually finds them, like the elder Duke duClermont who thought to use his position to mask his necromancy. But by and large, the great majority of nobles serve tirelessly to keep the rest of Andar safe in ways that they never even know about. Would you really look upon us any better if we were to brag about the invasions defeated before you ever saw them? What if I talked about the forays I've made on Andar's behalf behind enemy lines to forestall a new attack? Or the months of unending agony I endured to close a portal to the Plane of Pain years ago? There are countless ways in which all adventuring nobles have paid in blood, treasure, and effort which non-nobles never hear about.
I don't say this to gain sympathy or recognition - if that's all I wanted, I would be trumpeting my deeds constantly to all around - but to help answer your questions. I know it is unsatisfying to hear that nobles are working "behind the scenes", especially from my own time as an adventurer before I was granted title - but there is truth to it. The ways in which our deeds are seen is nothing compared to the daily effort exhibited by all of our nobility. Years of our lives are given to keep Andar safe, and at the end of the day that is the truest distillation of our duty.
-Lord Polare Lissenstine