What are the key component upgrades or swaps that would elevate the Boardman ADV 8.9 from a great gravel bike to a truly exceptional one, and how do different combinations of upgrades impact the overall performance and character of the bike? For example, would swapping out the stock wheels for a high-end set make a significant difference, or would a upgrade to a electronic groupset be more noticeable? Are there any specific components or upgrades that are particularly well-suited to the ADV 8.9s frame and design, and are there any potential pitfalls or compatibility issues to be aware of when making upgrades?