Well, I agree. With experience, it is possible to handle 13mil traces using screen printing. But think of newbies or inexperienced persons. A little over-etching can ruin the whole effort. Also your board has ample space for thicker traces to be accomodated. So I think these should be at least 40mil.

I will increase the trace width to maximum possible.

It would be nice if you can add a socket for an I2C memory since the users of this board will soon be needing to experiment the some advanced stuff

Great Idea, I implement this as well.

Also any GPIO port (no matter how many port pins it provides) seems useless without GND and VCC connections. External peripherals connected to these GPIO ports need these power connections in almost all the cases.

True, I will make provision for Vcc and Gnd for peripherals.

Some test points on the board might be useful as well like EA, RX, TX, +5V.

Very easy to ground the crystal case. I wonder why you didn't (must have overlooked :-)

And finally, you should provide the Silk and Mask layouts as well in case one needs them.

I will implement all above suggestions as well.

Regards,
Prahlad Purohit