> Are there any advantages over Visual Studio + Visual Assist, for C++ or C# languages?
A fully-extensible, flexible environment which anyone (even a secretary!) can easily extend.
> About text editor features, your workarounds have flaws compared to good GUI.
They're not workarounds; they are the features. emacs has a GUI. I repeat: emacs has a GUI. Tooltips in a GUI display as you'd expect. Folding in a GUI displays as you'd expect.
> Another text editor feature hard to do in text mode is spell checking for strings and comments. Color is already used for syntax highlighting, so wavy red underlines come handy.
Terminals support underlines!
> But visual studio is more than an editor, it includes a build system, debuggers and profilers, package manager, and many more related features.
Have you ever used emacs? It's more than an editor; it connects to build systems like make, maven, gradle, ant, what-have-you. It has its own elisp debugger, connects to gdb, SLIME provides an integrated Common Lisp debugger &c. It has a profiler. It has a package manager. It has a best-of-breed git interface, Magit. It has a best-of-breed personal organiser, Org-mode. It has multiple email clients (rmail, vm, gnus & notmuch come to mind, but there are probably more). It has multiple web browsers (emacs-w3m, eww, w3 & a new experimental WebKit-based browser). It has multiple image viewers. It has multiple terminals & its own shell.
Emacs is far, far 'more than an editor.' It's probably the single editor which is the furthest from being just an editor. Don't trust me: give it a shot! It really is a wonderful experience.
And yes, it has a GUI. Images, scrollbars, menubar, toolbar: the works. Runs on X11, macOS & Windows. And it also runs perfectly well in a VT100 terminal. You can use the same emacs locally and remotely, over SSH. It's pretty awesome.