I upgrade the device that needs the upgrade the most. Old, slow drive getting old enough that I need to consider reliability? Obvious upgrade. Old machine is lower capacity then I would like? High value upgrade. Which machine is going to see the most dramatic improvement? Let’s upgrade the old one first.
Makes sense to me.
As a side note, I have found using older laptops has given me a lot of peace of mind in truly using them “on the go”. I used to live in fear of my laptop getting forgotten at the pub when I grab a drink after work, stolen from the car, dropped as I dry to open a door with full hands, left in the sun on the seat next to me on the restaurant patio, having a drink spilled on it, getting fried plugging in to a sketchy plug in the customer’s warehouse, water damage in the rent while camping, and the like. I mean, who wants to risk $2000 to any of those scenarios. But having an old work horse, or a $200 steal I found online, or even the MacBook that I found at the recycle depot that only needed a $50 battery? Well, I am not nearly as worried about putting those machines at risk. As a result, intake and I use them everywhere. Oh, and I have them everywhere ( I often leave one in the car and have it when I find myself somewhere longer than expected. I have a laptop that sits in my young son’s room that I pull out while I sit with him at night sometimes. Super handy.
As a result, guess which machines I spend the most time on? It is the old ones. So upgrading the old machines actually has a bigger overall impact on my life.
My experience has been that, with Linux, old machines work surprisingly well for most of what I need them to do.