I like building decks so I often change them. People do scout you in tournaments, especially when you play the same group. Is it better to just stick one with one deck and tolerate being scouted to master the skill of that deck or just better to try and be an all around good player?
I see magic results (ignoring variance, which you can't control) as being made up of the following things in the following order
mechanical playskill > mental hygeine > decklist > inducing your opponent to make mistakes > information management
Keeping your opponent from knowing what your deck is can help, but it doesn't help as much as playing the best deck for the field, and nowhere near as much as playing a decent deck you're going to make minimal mistakes with. Even the true masters of vintage probably aren't playing at a level where scouting is a serious concern for them, compared to just playing the right cards, I know I'm not even close to that point.
I wouldn't worry about scouting at all. Picking the deck that you play the best, or the deck that makes you grow the most as a player, (or of course, the deck you enjoy the most) is where you want to be.
For what it's worth I tend to make deckbuilding and play decisions operating under the assumption that my opponent is going to know my entire decklist. I always assume they're going to make the right play with perfect information. I find thinking this way can cost you some % points in the early rounds of the tournament, but buy you some back in the later rounds where it really matters.