No, not all serves have some spin. A flat serve is indeed that: flat. One of my favorite serves on the deuce side is a flat serve right up the middle. Players know it's going there, but that doesn't make it easier to hit back. Plus I want them to cheat to the middle so that I can then spin (combo topspin & slice) it wide. I also like the flat serve out wide in the ad court, as the return generally makes for an easy put away.
The good pros will mix up their spins quite a bit. Also, they don't give away which side they are going to hit to. Thusly why so many people get wrong-footed by Fed.
The best way to fool your opponents, IMO, will be your toss. Keep your toss pretty much the same (again, ala Fed), and you will ace a lot more often. Some players you can tell where they're going as you will learn their so-called 'tells'. When someone throws it behind them, there is a good chance that they are going to hit a kicker to your BH (if both players are righties).
When I've aced the most was due to 2 factors: 1. lengthy serve practice sessions with cones, and 2. trading pace for accuracy and angles.