I went to an old-school language school where I was forced to take tests in handwritten Japanese. I probably still have some of that in my brain, but like you, I almost completely abandoned it as soon as I didn't have to take language school tests anymore.
It's occasionally useful to write out a character, but on the whole, it's completely unnecessary now that we have computers with hiragana keyboards.
As a partial aside, the Heisig anecdote that leads off this piece is painful:
> Japanese children learn the spoken language first, then they learn how to write it in elementary school; Chinese students of Japanese (who tend to be pretty good at it) have pre-existing knowledge of character meanings and forms from their mother tongue, so they only have to learn how to pronounce them. Therefore, a Western learner should first focus only on the meaning and writing of those couple of thousand common characters and, only after having mastered those, should move on to studying the pronunciations.
Going from "Japanese people learn the spoken language first" to "you should spend a big chunk of time learning characters before learning sounds, words or grammar" is a pretty remarkable mental backflip.
The author says he spent eleven months doing this before devoting any time to the spoken language. If I could put the "head exploding" emoji here, I would do it. I spent only slightly more time than that at language school, and came out conversational.