Too Many Queens?

You are saying you want to break a rule of chess that is from a long long time ago?

Watch out for stalemate if you have more than one queen.
Always give a check, this is a simple method to avoid stalemate.

There will be very few serious level games where one side has more than one Q on the board. Promoting for the sake of it is a feature seen in beginners' games
There are practical positions where you're going to have more than one queen, though most of the time it is only briefly. For example, there are some opening variations where you sacrifice your original queen to quickly promote a pawn. Some of these (and I've played a few of them) promote the pawn just before the original queen falls.
Alekhine had a number of games (including one during his World Championship match with Capablanca) where both sides had multiple queens.
The point is, though, that you should only queen pawns when it's best to do so. If your opponent has just his king left, one queen will allow you to checkmate more quickly than taking the time to promote a second pawn. The longer you stretch things out, the more likely you'll make a mistake leading to stalemate.