The thing is that I get a different feel for the game with each chapter that I visit. The main thing that makes it 'feel' like Alliance in every chapter are two things. First is that I'm playing the same character that has built up a reputation and connections within the world. So when I head up to Seattle and run into Baron Polare, it has the feel of the Alliance in the game. The second thing is the rulebook. Seeing Half Orcs, having anyone who casts Necromancy as being evil, no religious figures, Dragons being the most powerful beings in Fortannis and Fae being their equals when they're in this realm. Yes, the amount of treasure policy, how I have to fight in order to bring someone down, that I can completely die twice before worrying about it and all of the rules also gives a feeling of Alliance.
And technically, I also believe that if some group of people who never played Alliance before picked up the rulebook and begun running events, it would feel like an Alliance game. It may not fit in with other games flavors 100% but that is due to individual chapter flourishes added to the game. I could go to that new, independent game and know what to expect from Hoblings, Kobolds, that I can still dodge X number of attacks while my Dragon's Breath does 40 points of damage and I should be arrested if I cast chaos. So it would feel like an Alliance game. But at the same time, I could go to a NERO chapter and have it feel 'Alliancey' because of the system, races, combat, resurrections, etc.
However, I do not believe maintaining the feel of the game equates to making the game better. The issue becomes what one person considers 'better' is what another would consider 'worse'. For example, I felt the introduction of the Shatter Spirit carrier would (and does - again IMO) change the dynamics of combat so that people aren't just running forward, slaying everything in front of them with full knowledge that a simple cure light spell/potion/alchemy/etc will bring them right back up. However, when this was brought forth in a past national event, some players had very negative, physical responses to it.
You'd want to maintain the basic setting, storyline, background, laws, etc. But the mechanics can (and have) changed over time. There was a pretty good change a few years back to the rules (such as being able to deliver backstab damage via ranged weapons) and it seemed to improve things overall. The rules may change but as long as we're in Fortannis, it will be Alliance.