The pro has an enclosed print volume and a few minor mechanical upgrades. It's also usually in a metal frame that gives it the stability to print at 0.05 mm layers.
And let me tell you now: you will NEVER print at 0.05mm on a flashforge. It would take a week for a smallish print and wouldn't look much different from a print at 0.1mm.
Personally 0.2mm is my normal hi resolution print and 0.3 my standard.

The creator x is a great machine. I've got around 1000 hours on mine. I mostly print things that don't take too long. So that probably equates to close to 1500 actual print runs and a lot more objects than I realised I'd printed :-)
A lot of the small stuff gets given away anyway, or binned if it's an early iteration of a design.

Apart from adding a cooling duct for the print area, all I've done is add a flat printbed - basically because of the way the printbed is screwed to the heater - it'll warp out of true very quickly. A 225mm by 150mm by 3mm thick sheet of aluminium taped on top of the orginal is what I use.
You can use glass if you want - but it's a fairly safe bet you'll need to use something.

And apart from greasing and cleaning the rods every few months and the occasional bolt tighten, that's basically all I've ever done to her.

The only thing you'd gain from replacing the motherboard is the abiltiy to use a few different slicers. But I've found makerware and simplify3d are all I've ever needed.

Not sure what you'd gain from changing the extruder. I haven't found anything yet I can't print, from ninjaflex to polycarbonate.

If what you want to do is buy something to upgrade - you'd probably be better off starting with an iprusa I3 base or kit.
Cheaper and designed for infinite tinkerability :-)