Everyone is entitled to their own opinion here, but as for Vietnam's culture supposedly not being "East Asian," I would have to regrettably tell you that you're incorrect on that point. Despite being geographically a Southeast Asian country, Vietnam is widely considered by many factual bodies and reputable sources to have been highly influenced enough by Chinese culture to be considered part of the Sinosphere.
As for the analogy about the building, I believe that it's not as black and white as you presented. The problem here is that the building is not perfectly suited for Vietnamese, and so by restarting on a new canvas completely, you can create a system that is tailor made for Vietnamese. Because of Quoc Ngu's young age, that means there isn't as much momentum behind it, meaning it would be easier to "abort" now than later. I understand what you mean when you talk about a country with limited resources, but I never said that this should be the main focus of the country right now. I am simply thinking wishfully, and maybe the issue of script will come up sometime in the future when Vietnam gets on some better footing.
Many Eastern Asian values have already been etched into Vietnam's culture, and it would only be natural for it to continue on the same "cultural route" on which it already treads. Even if Quoc Ngu is "working," that doesn't mean that it should be the end-all solution for the language. If languages were just about "what worked" and nothing more, then we'd be faced with a lot more countries with the Roman alphabet system. For example: Pinyin has been developed far enough to completely replace China's current writing system, but it hasn't. Why? Because there China retains some of its "pride" towards its national heritage. Japanese can be easily written with the roman alphabet, perhaps a version that is slightly improved from simply current Romaji, but yet the Japanese still stick with their Kana + Kanji. The Japanese have resisted a Western script and have stayed true to their "national heritage," even if it clearly has Chinese influence. Therefore, it is reasonable to say that the Japanese, even though they enjoy distancing themselves from China nowadays, recognize their close ties with Chinese culture as something innate to them, and I am of the opinion that Vietnam should too.
As for a script having East Asian influence, I don't see any problem with it. In my opinion, it's certainly leaps and bounds more culturally "accurate" than Quoc Ngu, but I'm sure the BEST solution overall would be to create a script tailor made for Vietnamese. And, even if it does have remnants or influence from Chinese characters, it only makes sense; Vietnam is part of the cultural Sinosphere. Look at Korea, one of the main reasons why they look down on Hanja is because of its ties back to China, yet Hangul itself (which you should consider to be tailor made for Korean) still has obvious Chinese influence. Heck, some of the parts of their script are Chinese characters in and of themselves.
On another note: As for the geographical location of Vietnam, there is even debate as to what really defines the geographical location of countries that span more than one "region." If you look at a map, there are no distinct lines that separate where Southeast Asia starts and where East Asia ends. Rather, people just group countries by their borders for the sake of organization by nation. If it really were a case of some definitive line, then you would consider Taiwan a part of Southeast Asia, or North Vietnam to be part of East Asia. It's all a really confusing matter, but it's not the topic of discussion here anyway