Should you reveal who was a spy and who wasn't at the end of a game?
I've never seen a single player (spy or not) being able to avoid cheering, asking "why you did that" or commenting a recently won/lost The Resistance match. This is an important moment of relief, discussion, curiosity satisfaction and laughter. It's like sharing an adventurous or humorous story with those at the table, maybe strengthening or creating friendship bonds between people.

It is true though, if you play this game a lot with the same group, they might find it easier to know if you're telling the truth or lying... but they will never be sure! And if you think they are, you can try to change your behaviour. One way to achieve that is to know what people expect you to do in certain circumstances, and to get to know that, you can talk about a recently played match. You can also try to copy or remix with your own approach another player's strategy, something that he also might tell you when the game ends. Bottom line: reinventing your play style and avoiding being obvious is also viable through conversation and experience exchange.

Keeping things secret allows you to keep your strategy to yourself and not being able to know what others know. Although mystery is also fun (The Resistance is all about mystery), I find it hard to understand how this way of being mysterious could be better then sharing the experiences in typical The Resistance play sessions. I must also add that some players might even end up frustrated, thanks to not being able to talk about what he and others were thinking.