I think the reason for me at least why I would use ninjatrader is for order management and charting. If you want data feed, it is better if you use the broker data than ninjatrader. Since I trade with tick charts, I need a better order management ...
My trading style hasn't died yet. I don't believe it will; at least in short term. My trading style is dynamic. You learn this with time and experience. I also think that high frequency trading did effect the movement of the market.