Voiced protagonist is obvious. It shouldn't even need mentioning that having the protagonist voiced is a universal plus. By definition, point 2 is a quality that allows a protagonist to be 'not just another worthless non-person protagonist', so again, a plus. In my opinion, if the heroines are voiced in ANY VN, the protagonist should also be voiced... but if you like your protagonist to be a non-person cipher with no personality, that's your business.
Point 3 is purely personal tastes, I'll admit openly. However, it is a commonality to all good trap protag charage. Probably because most ojousama protagonists in JVNs tend to fall into the yurufuwa (think sweet-mannered airhead), arrogant (often combined with tsundere elements, for some reason), or elegant archetypes, all of which are good archetypes for creating atmosphere.
Point 4... completely glossing over the drama of a cross-dressing revelation stretches suspension of disbelief by definition, even beyond that of a cross-dressing guy infiltrating a girls' school. While no one seriously thinks any of this is realistic, suspension of disbelief for the purpose of enjoyment is a necessary process to enjoy most fiction. Oh, I'm not talking about drama on the level of Tsuki ni Yorisou Otome no Sahou's normal/bad end, but rather the kind of drama where there is real tension on one or both sides of the equation. In my experience, when all or a majority of the heroines sort of just blink and say 'that's fine' without even thinking about it, it is a serious mood-killer.
5. This is just a common comedic point that creates internal laughs for fans of the genre... and having built-in jokes is always nice.
In the end, points 1, 2, and 4 contribute the most to the quality of the works in question. 3 and 5, as you mentioned, are mostly matters of taste and commonality.
Well, if you actually wanted an answer, there is your answer.