1) replace Qt memory management with TR1::shared_ptr (or boost).
For the core purpose of Qt (GUIs), Qt's various memory models work very well. Every widget is a QObject and by default they fall into parent child releationships that include life-cycle management of your objects.
Why would you want to mess up that clean model?
2) replace Qt collections with STL collections.
Another unnecessary generalization. I actually much prefer Qt's collections because A) they are implicitly shared (you can pass them around without getting deep copies) and B) they have one clean and very efficient implementation across platforms, so I don't have to worry about the memory and performance characteristics of a MSVC std::map vs a GCC std::map. Also they are much cleaner to work with and don't require hideous iterators every step of the way.
3) replace Qt threads with boost::threads.
Again, Qt threads will perform as good as native threads on each platform, something you can not guarantee with pthreads (with weaker windows support). Also, QThread and friends (QMutex, QSemaphore, QWaitCondition, QThreadStorage) are very C++ oriented and stylistically much cleaner than pthreads and even go beyond it in scope.
4) replace Qt signals and slots with boost::signals.
This is probably the most valid argument, and there is some legacy reasons why Qt had to throw a meta object compiler on top of C++ to get this to work 18 years ago. But in the mean time, that moc layer has paid off in gold. Now you the ability to get free introspection on classes of your choosing which is vital in making C++ suck less in well designed programs (i.e. can do automatic class instance serialization etc).
In other words, make Qt play nice with STL and boost, which are the foundations for developing C++ code these days.
In other words, Qt is a great one-stop-shop for cross platform development and I wouldn't change a single thing you listed. In fact, if you write your C++ code in stylelistic keeping with the Qt libraries, you avoid most of C++'s warts and can even enjoy the language.