One can argue that building an amp kit is a good experience, but its really nothing more than a parts puzzle with little learning involved. To learn the secrets of tone buy every cheap tube amp you can find and learn to do maintenance, then service, then mods with a collection of used parts. That's how boutique amp builders find their start. The resale market is full of built kits that sellers want top dollar for, but buyer beware it may or may not approximate the sound of the original article made to era-consistent quality standards. That's why vintage matters.
Not just vintage, but brand names matter. Because it does, if resell value is any potential part of the equation.
Every player says they're never gonna sell their current amp of the month. New, old, vintage, boutique, home-built, whatever. What doesn't eventually get sold gets picked apart and/or becomes landfill. I don't make the up the rules. I only observe them and plan accordingly.