The only problem is that I don't fancy writing code and testing for the two people who actually think the GX4000 is a good machine
Oh, come on

Although to be fair I looked into the GX4000 to make a special edition of Magica and looks like is more involved than I was expecting and... I gave up (sorry). And I don't have a GX4000, so I'm not one of those two

I wanted to add to the conversation that, at least in my case, I can't really afford the time to fill the extra memory that those 128K provide, specially as a solo developer.
I rather make 2-3 games a year than just one super-production that, at the end, is still a CPC game that has limited audience. I'm OK with putting 2-3 months of my free time on a 64K game that people may (or may not) play for a week, but it would depress me a bit in a 6+ month project

Some people around here will always ask you to use 128K, use extensions, put more content, more time, go bigger! like that was the sole objective of making games for a 30+ years old machine

So I still think is up to the developer; do whatever you want with you game!