I had my own thoughts on a reconceptualization of the Romulans for TOS+:
Romulus is a good free world where the civilians live good productive lives and they just happen to be antagonists to the Federation WITHOUT being so obviously bad. I mean as it stands they never really delved deep enough into the Romulan culture anyways and they used the Military Dictatorship stuff for the Cardassians (to their benefit). Why not have the Romulans turn out NOT to also be a Military-Ruled Empire but a pleasant place that just happens to oppose the Feds?
The Romulans can be a democracy that respects its' people without having the exact same values as the Feds, perhaps they see it as okay to go around settling on worlds with native populations and interfering with their development as long as they get a new world. Maybe they just feel they have a manifest destiny (which is pretty much canon...) and the Feds are an obstacle.
And the Tal Shiar would be respected and seen as a necessary and noble force by the Romulan public for protecting them from external threats who would subvert Romulus and from fellow Romulans who want to undermine and subvert all that they have built from within. A nice contrast from the Obsidian Order (who are feared and hated by nearly all Cardassians).