But the greater problem is these 3D printers are not plug and play. Everyone I know that has one is constantly f**king with it to get it to produce the appropriate results. And because it is a long process to print something, one mistake screws up a whole print.
I think they will never be plug and play. Even the big, expensive, professional machines aren't. The problem is that people call this "a printer", evoking the idea of a cheap-ass inkjet that you connect to an USB port, install drivers and it works.
A 3D printer is a CNC machine, more comparable to a CNC router or a CNC lathe. And those need maintenance, alignment, repairs and skilled/trained operators as well. Expecting a CNC machine becoming plug & play is pretty much an utopia - it just won't be cost effective to do so. The user requiring "plug & play" likely doesn't have the skills to use one of them (effectively, not just by downloading files and pushing a button) anyway. Those people are really looking for a Star Trek replicator, not a 3D printer. Unfortunately, those don't exist yet
Even a commercial, production grade CNC router needs to be homed, needs to have endstops adjusted, needs cleaning, oiling, replacing worn parts, etc. And those machines are built way more robustly than the flimsy plasticky pieces of junk in many of the mass-marketed 3D printers. Heck, the original Printrbot was made from wood held together by zip ties!!!
Now, some machines are certainly better than others, but you won't find one that doesn't need tweaking and adjustments. It is just par for the course. If someone is looking to buy a filament based printer these days, I would strongly suggest looking for a RepRap derived machine - at least if something goes belly up, you can find replacements easily and cheaply. Good luck repairing some of those big buck commercial ones! I have a Mendel90 myself and it works quite well. There are some issues I may replace/improve later, but so far it works.
Also, a sub $500 machine is going to be crap almost by definition. Just the mechanical parts - slides, motors, extruder, belts/rods and chassis are going to cost that much new. So if a machine is cheaper, then corners were likely cut somewhere.