Depends on what you are shopping for
If you are looking between an A4 and a Jetta yes there are resemblances and a top trim Jetta is still a very nice car
But there are cars you can't get from VW.
Audi RS4, S4, S5, RS5, S6, RS6, R8
Audi is the upscale Jetta just like Acura is the upscale Honda. Infiniti is upscale Nissan. Lexus is upscale Toyota, etc.
You could argue that certain Audis are poor mans Lamborghinis. Soon Porsche too since VW owns freaking everything.