Two issues: One, simply getting value for $. I'm amazed at the cheapest componentts used in speakers that are not inexpensive, and I enjoy him examining that and calling them out on it. If you purchased a Rolex, and it kept perfect time, and you found out someone had swapped out the movement for a cheap Seiko movement, would you have a "what the heck is the difference?" response on that? I know I would not. If I'm paying X for a speaker, I don't want to see the cheapest possible components inside regardless of how it sounds, unless it's a cheapo speaker.
Second, in some instances his changing X over components, adding more dampening materials, slight changes in where the X over frequency happens, does seem to result in improved objective performance. In that case, for some, perhaps worth purchasing and installing his upgrade kits. That's up to the person and how much with want to invest in a speaker. Will it be audible? In some cases, it makes sense it should. For myself, I would not spend $300 to upgrade a $500 speaker.
As mentioned in another response, was dissapointed and surprised to see him go down the speaker wire/power cord rabbit hole.