Astronomers hate putting lenses into their optical systems--there is always some light lost to reflection off the glass surface. The VLT is an 8 meter diameter telescope, so supporting a giant lens above the telescope would be a major engineering issue. This isn't really a problem you can solve by adding a new lens or tweaking the secondary support structure--it's a fundamental feature caused by the wave nature of light. Anytime light passes through an aperture, it creates a diffraction pattern.

Um, no. The spikes are caused by the diffraction of light around the struts supporting the secondary mirror in the telescope. The wave nature of light ensures that no matter how large you build your telescope, you cannot focues stars to a perfect point.