If I were to go after printing the smaller things with great detail I would retool one of my printers to have less teeth on the drive pulley for each of the belt driven axes(20t is common 16t means more steps per mm of travel) and a finer thread pitch for the leadscrew driven axes. Then I would chase down the 400 step/rev or 0.9 degree stepper motors. Finally I would bring it all together with a 0.25mm nozzle. I might also design and make some careful frame supports or reinforcements. The reality of these mods will mean notably longer print times with the distinct tradeoff of higher resolution printing. And so because of what these mods do to print time, you wont find too many printers sold this way as they would be at a serious disadvantage to their own competition. So what you need is an open source printer that you can easily change parts on and recalibrate. Because there are high res printing parts out there. You just need to be able to identify them and then adapt them to your printer.