Welcome to the Miyoo "club".

Charging... stick to the cord it came with and buy one of these CHARGING BLOCK

Static sound... I think I have heard/read that this is an issue when the volume isn't full? I don't really notice it so much.

Plastic - I think you will be fine as it is a non flip device. Should hold up.

SD card cheap - yeah this is standard. I mean these devices are so cheap as is. Not sure we should expect them to come with a $15-$30 quality card. We all upgrade from all handheld companies.

Bluetooth. For headphones? I say get some retro headphones that have the orange foam and wire and really have that old school vibe/kick. haha. To be real I don't know if I would ever use bluetooth on one of these. When I am in public I have my device on mute.

As for upgrades... the speaker is just fine on the Plus models and the "upgrades" that most were doing for the mini are not really worth it on the Plus IMO. I would say that swapping out the ABXY buttons if you don't like the maroon on the purple and then adding some lube would be a nice upgrade/change. I just did all black buttons for a friend on his purple.