Wouldn't be without mine, just a budget Creality Ender but have made everything on it from replacement fan on a jig saw, lathe change gears, saddle stop, chuck spiders, nudgers, spacers, Stephenson's Rocket, servo frames for RC gliders, patterns, moulds, sundry replacement bits for broken/missing 'things' round the house and on and on…lost track really.
They could all be considerably improved with some effort, but despite various plans to improve my Ender it is still pretty much as it came out of the box… because it just delivers consistent output in the 'good enough' spectrum.
In future, I hope there is some improvements in media technology addressing issues such as strength, bonding, stability etc. Ideally for a structural product, we would like a filament with the strength and stability of nylon or polycarbonate, the ease of printing and resilience of PLA and the post processing properties ABS.