There is an old saying:
First time is a good trick - second time is a good lesson.
Magic has a handful of effects that can be done under the command of "do that again" - some using the exact same method - like a bill change - some different - like an ACR.
The thing is this - not ALL effects can be done twice - and that doesn't make them weak.
It would be like watching a movie twice, and having the same reaction - you will find something new every time you watch. Moreover, you certainly won't be thrilled with the ending like you were the first time.
Here is an example from Youtube - the awareness test. Watch it twice.
http://www.youtube.com/watch?v=Ahg6qcgoay4
If you can't see it both times...you may be retarded, but it doesn't make it any less interesting.
Saying that a good effect shoudl be able to be repeated - is like saying - a good fighter should only be able to use his hands...sure, maybe, but I believe their is no such thing as a fair fight...WHY would I want it to be even odds of getting my butt kicked. I want to make sure the odds are tipped in my favour.
The same is true in magic - every advantage - and the element of surprise is certainly a big one.
So to conclude - magic should appear moveless, but repeating ANY effect is not the measure of it's quality.
Interesting topic though.