My goodness, I could have written this word-for-word. Similar age, same Apple II BASIC and 6502 upbringing (roll sleeves and call -151) and also wrote to Infocom. We were in the UK so even more surprised to get a reply similar to yours several weeks later. Sadly my letter is also lost to various house moves. Or eaten by a grue.
Me too, except my letter was to Sierra On-Line and my experience was on TRS-80 6809. Really classy reply asking me to write back when I finished school.
I recall sending a letter to them asking them for information on how they compressed their images for their hi-res adventure games. While they replied, they said it was a trade secret. I was kind of bummed. But being a 12 year old kid who barely understood the 6502, it probably would have gone over my head.
Lovely to hear this about Infocom and SOL. The former was my obsession throughout the mid-late 80s on my Atari 800XL, and then the latter for the next few years after getting a 386SX in '89.