throwing a nano in my car soon
- I think an upgraded voltage regulator on the VIN pin would be my #1 "want".
An automotive-grade pre-regulator should solve that problem.
- The next one would be better 5V and 3.3V regulators for more stable voltages on my digital pins
There have been a couple posts recently where people don't seem to understand the essence of "digital" logic, or the nature of voltage regulators. Digital logic has 1s and 0s that are "non-critical: in their exact values. You can't count on getting "stable voltages" out of digital pins. You can only count on them being with the defined range for 0 or 1.
- and as reference on my analog pins (right now I can't rely on the accuracy of my ADC readings).
That's a different matter, though I think it's more likely to be related to noise on the actual analog pins than problems with the voltage regulators. You have to get prety specific with your requirements, though. a 10bit A2D nominally requires a 0.1% voltage reference to give "accurate" results, and those tend to be expensive and the opposite of "robust."
The 3rd thing I might want is higher quality oscillators
More accurate? More robust? One of the reasons that resonators (~0.1%-1% freq accurate) get used instead of crystals (0.01% accurate or better) is that the resonators are more physically robust...
the ability to draw 20mA on a few pins without experiencing voltage depression.
"ye canna change the laws of physics..." High current IO pins on microcontrollers are going away, rather than getting better. And see (2).