Hello Mollytee,
The main difference in Advanced and Extension is basically the depth of knowledge required. For Advanced, you're basically brushing on 3 modules, most of which focus on different aspects of understanding and analysing texts (e.g. Mod A is about comparison, Mod B is about critical analysis and Mod C is about representation).
Extension, however, requires you to know in-depth a specific value, context or genre. It's more than just knowing the techniques and linking it to your analysis (which you can get away with slightly in advanced). From your understanding you need to synthesise a creative and analytical responses that shows the marker your knowledge of an entire, very complex module. Extension really builds upon the skills you learn in advanced, namely:
Mod A (comparison): linking your texts together, understanding how they are different and similar to construct a unified argument in relation to the question
Mod B (critical analysis): Basically EX1 relies a lot on critical thinking skills, where your knowledge is tested a range of contexts (analytically and creatively)
Mod C (representation): Well, it's in the creative as well as understanding the significance of how each other tries to represent his/her concerns.
This is my broad understanding as well as my experience doing EX1.
And I think the gothic genre remains relevant to readers today as it represents a period of human history. Remember texts are like a time capsule: it preserves popular ideas and cultures from when it was written. I remember doing this genre in year 11, and I think what makes it very relevant is how it reflects the fears and worries of the past, which quite poignantly is still what we fear today. Sure, all texts, not even gothic ones, tackle some sort of dilemma that is still relevant today, emphasising the universality of the human condition. However, classical gothic elements that are integrated within famous gothic texts show us how the people of the time uniquely reacted to these concerns. This paints a brilliant picture of how far as a race we have gone and how much we have stayed the same.
Hope this helps
Good luck!