I agree with everyone's suggestions.
The positive side of "more active" nobles should also be emphasized:
*there are some bad ones, but some good ones too, most are in the middle; and most know the reason why they're still alive and allowed to be a noble is because the commoners don't hate them so much that they get together and overthrow them;
*they can call for help if the fortress is threatened, and it will probably come;
*they're skilled fighters, can organize the fortress defense, rather than relying on a militia, and their guards can help defend the fortress; primarily, the nobility should be a military caste, rather than a caste of rich parasites (of course, there are exceptions);
*assuming they're kept happy, they're perfectly content to let the commoners run the show; mayorial elections and managerial decisions still go on as always, common criminals are sent to the cages, chains, or the hammerer by the Sheriff's court.
*sometimes they might be motivated to start a metallurgical industry, expand Dwarven vintnery or explore the under-ground river, or even go hunting for hidden fun stuff;
Another dynamic that I would propose is that only the fortress guard can be used as soldiers with real weapons (of course, individual dwarves can fight, and defend themselves) until a noble arrives and militarily organizes the fortress. The fortress guard should be the stereotypical "band of peasants with torches, hoes, and pitchforks" led by a sheriff, who could be a minor swordsman; they should behave much as a squad of dwarven soldiers does now--run around scattered, return to the mess hall if hungry... they shouldn't be able to bear real arms, except for the few hunters, just farm implements or tools
When the noble arrives, he organizes the Dwarven Militia, which can turn dwarves--with drill, weapons, armor, lots of physical training, and plenty of time, into several squads of fine soldiers, able to face down even a great and numerous host of goblins.
This would be the nobility I'd like to see.