At the moment I said the words, I flashed back to an incident long ago when a friend said those same words to me -- and what a negative impact they had on my excitement and enthusiasm.
The moral of the story is that one of the biggest obstacles in a company's encouragement of new ideas and innovations from employees is management's "We've already done that" mentality. Of course, it's true that if you tried to grow a tomato plant in December, it probably wouldn't grow. But maybe if you tried to grow it in May, it would. Companies that reinvent themselves (or try previous ideas with new implementation) are likely to be positive, progressive and, quite possibly, profitable.
Maybe another angle is to remember not to stop doing the things that made you successful in the first place. "Old" ideas wrapped up in creative efforts and enthusiasm can result in "new" avenues of achievement.