Some of the fare at Hong Kong Restaurant was indeed up to snuff. As you say, the turnip cakes were excellent, the best item on offer in fact, and the dumplings were for the most part pretty good. I remember thinking that the steamed pork buns were lame, and there were a couple of other items that didn't quite cut it. In general, I would give Hong Kong Restaurant only a "B" because the food lacks the clearly defined and distinct textures of a really good dim sum house. Everything tends toward a low-grade mushiness if you know what I mean, rather than being distinctly springy, or slithery, or puffy, or whatever. I believe that dim sum is primarily about this diversity of texture. My favorite dim sum house and perennial standard of comparison is China Pearl in Boston.
I will certainly report on any further findings. The folks at Asia Market in Durham also recommended a place called Pao Lim, which is only a couple of hundred yards down the road from the grocery. I haven't been, but would interested to hear any scouting reports.