Welcome to AC!
The upgrades are a way to take the base kits from hi-fi to audiophile using even higher quality parts than even the base kit, adding clarity and detail, so long as your overall setup has a means to take advantage of it.
I have a mostly base level kit, with my only upgrade being tube connectors which i installed a few months after building a base kit, and it was already worlds better than almost anything ive ever heard.
That said, if your main goal is to just enjoy rock/metal in the workshop and not for "serious" listening with high-end gear, then the base kit is all you really need.
Should that ever change, the base kit still has A LOT to offer when you feed it a better, cleaner signal with quality cables & hardware, before you even need to consider an upgrade to a crossover or tube connectors, but tube connectors are a killer first step to take in the future if you want to see if its right for you without doubling the price.
Hope that helps!
