If you micro your sniper, it will inflict far more than its price in MP damage, without the opponent being able to retaliate. So yes, it's very much worth it.
That is exactly the problem, you have to focus on controlling few super units instead of enjoying flanking with infantry.
Well, I do it and it works. Ooorah means they either have to follow you and abandon their ground, or hold it and let you cap. On some maps (Langreskaya especially) it's easy to run straight to their cutoff. The sniper arrives soon anyway, and once he's their its open season.
Ooorah is good but if you are building a sniper early you will not have the conscripts needed to do what you are saying. You need 3-4 conscript squads to do that and its not possible to get all of them plus early sniper.