The waiting game is for those who are afraid of 'buyers remorse' and there will always be a 'newer better gimmick' down the road at some given time.
The technology on these things is pretty solid right now, and the manufacturers are having a real tough go of trying to invent some new feature to entice us to buy a new phone, or new car, or ??
The Galaxy S5 is a very solid performer and the feature set is pretty awesome right now. It will still be a solid performer and be a strong contender this time next year.
right now, there is the S3 and S4. both very good phones. The S4 is almost as big as the S5. A friend of mine has the S4 and I played with it for a while a couple of days ago. The screen is a tad bit smaller, but it would do just about anything that the S5 does. The pictures it takes look great even though they have fewer pixels.
My previous phone is a Galaxy S and I used it for 3 years while watching the S2, S3 and S4 phones come along. None of those phones offered me enough to make me want to turn loose my dollars and buy a new phone. It is still a good phone, I use it on WiFi to read the news of the world, get local weather reports, etc.... It is always by my bed if I forget and leave my S5 in another room.
So, go for it, get the S5 and learn to use it. IMO you will not be sorry.