The hypothetical conflict between mayor and heroes doesn't play out the way many are describing in my experience. The Mayor is a politician and will act within their capabilities. The heroes will do their stuff and community benefits may well follow, encouraging exceptional exemptions. Mayors vs heroes only works at lower levels and at higher levels it become a case of so what? 11th level heroes smacking up the Mayor of a village are actually confronting the hierarchy of the land. The village isn't going to be the problem - unless the adventure is in FR.
Regardless.
My character has developed a stronghold and it's very cool.
The actual fortifications and garrison are not to stop a determined attack from a foe that is a credible threat to the heroes. No. Rather they are designed to force the foe to expend a portion of their resources to bypass it, while revealing at least a portion of their capabilities, and exposing themselves to a poor positioning on the battlefield, of the defenders choosing.
The stronghold can offer the defender: superior line of sight, height, cover, time to buff, better maneauverability, flight platforms etc... The attacker otoh is constantly inconvenienced, which may dissuade a similarly powerful foe from chancing thier luck.
The stronghold will function normally versus the standard humanoid invaders. In effect the rank and file fighting each other acts as an environment for the warring heroes to battle each other in. A hero needs to be careful not to reveal their hand on the many tempting diversions. Basically the 5th level fireball caster is smart enough to know that their first fireball may be their last once it reveals their presence.
A recent battle we fought versus a Red Dragon and his half Dragon sorceror rider was above my hero's stronghold. We were able to flee within to escape the flames and heal. My hero's cohort was able to discretely counterspell through the arrow slits, and we were able to sally forth from the different towers. It also encouraged me to better design the towers.
OoC the stronghold has become a place to defend. That means it needs to be threatened but at the same time it is an invaluable hook for a style of play and thus should not be destroyed. The defensive adventure is pretty cool.
As for taxes and fealty, well, the stronghold in a Greyhawk type world comes packaged in politics, patronage and tithes. The financial situation should be a nett win but with heavy costs cutting into the revenues. My hero's stronghold has less of the above because it is well beyond the borders of civilisation. That has meant he had to cut costs by allying with Gnomes, Dwarves and the resident Druid. Oh well, that's D&D, everything's included.