It depends on the popularity of the area and development really.
The price of the homes on our development didn't drop at all- the incentives just changed. For example, when the last couple of plots were available, they started to include things like "premium tile package" and "turfed lawn" but advertised prices never went down. I can't speak for what happened during private negotiations.
Something to also consider if you're planning to hold off is how many of the type of home you would like are available and where those plots are. For example, there may be 100+ homes, but there were only 3 of our type of house on the whole development. Each were on very different plots.
Plot wise consider things like views, parking, through roads, bin collection points, public footpaths, what the plans are for the road and surrounding roads on the development in future (bus stops, shops etc) What way will the garden face, where will you get light?
Look very carefully at what each plot offers. The best plots do tend to go quickly.
The reason we ultimately went for a new build was for the convenience of the sale. We needed to be moved in by a certain point and couldn't guarantee that if getting into a chain with an onward purchase.
We've had older properties (100 years+) newer properties (50's and 80's) and now a new build. We're enjoying the comfort of knowing any problems will be sorted and that everything is new so should last a good while and meet current regulations and energy efficiency guidelines. Older homes had many surprises for us (bodged DIY, unexpected things breaking etc). Our old, old house had character but was a lot of maintenance and work and horribly energy inefficient.
People do knock new builds but it does depend on the individual development and site manager as to the quality and finish. With that said, if you're planning to move within the next 5 years, definitely don't get a new build. It takes a while for the pricing to level out in most cases.