Hi, sorry for the delay in responding. I'm prepping for a trip to Shenzhen, China, and a bit overloaded right now.
The LED matrix seems better on the SmartMatrix as well. LED diodes seem to have more brightness range
This is due to how the panel is refreshed, not the panel itself. The SmartMatrix Library uses 36-bit color for refresh, with a separate global brightness control. Pixel is limited to a 9-bit color palette.
May I ask which one it uses? Is it an Adafruit matrix?
It's very similar to the 32x32 6mm panel sold by Adafruit, but I use a different supplier.
I might want to upgrade it to 64x64 at some point and if I do I'd like to get the same LED matrices.
Could issues with that: the firmware for the SmartMatrix Display is set at 32x32, you can't expand. If you use a SmartMatrix Shield and Teensy, you can drive up to a 64x64 panel, but it won't look as nice: 24-bit color and lower refresh rate (~90 down from 120Hz). You probably want to buy 4 panels not just 3, as LED colors vary slightly from batch to batch, and you might notice the single panel sticks out from the rest of the batch, e.g. it might have a slight green (or other color) hue, as the color balance doesn't match the other panels.
I'll need a larger acrylic diffusion sheet in the front though to fit with the larger frame
This writeup shows a lot of details of how to build your own SmartMatrix Display, the acrylic is in there. Let me know if you have any more questions!