For me? Yes. When it's in the case, it's done. Usually when I'm planning a build, I start with the idea. Then I grab a plastic tray and head for my parts bins. I pull everything that might go with the idea. Bag everything. Build model. That way there is no second guessing later.
Now I'm not saying that there aren't circumstances for me like you described occasionally, but it usually involves a "I'd really like this style side mirror for this build", so the model is done and the mirrors added when they finally are located.
As for dusting your models, thats great. Dust is a killer of paint jobs. However with no other options, I really do recommend the acrylic model cases. With the 40% off coupon they are only $4.50 at Michaels. Buy one every paycheck and soon your whole collection will be saved the hazards of dusting and you can stack them, so more models per shelf.