Actually, there is quite a bit new in mechanical engineering. You may not be aware of these advances because these things to do not necessarily translate into consumer products or marketing, despite the fact that they solve useful problems and improve our lives.
In materials we have composites, which are extremely strong for their weight. Tough to design, though. Like computing, this started around the 60s and has become more and more sophisticated. The Boeing 787 and other planes use modern composites to greatly reduce weight and save fuel. We have much better steels and other metals than a generation ago, for example google dual phase steels.
Biomedical engineering is mostly mechanical engineering; it involves the design of medical implants. Modern materials can make stronger and lighter replacement bones such as hips. Artificial organs are on the horizon, a real artificial heart has been built and used successfully.
In fluids, we have much better and more optimized airplanes. With computers and the Finite Element Method (FEA), aerodynamics has become much more quantifiable and less model testing is needed. I'm actually glad that aircraft have not been sold at the amateur, consumer level. The way people drive in North America, flying cars would end our so-called civilization. Fluids has also helped design more efficient engines and generators.
All the things I mention solve real problems, and may be classified under the umbrella of mechanical engineering. Its a broad field, so abit hard to define, but in my view anything that requires non-trivial application of mechanics, materials, or thermodynamics can be called mechanical engineering.