"...the obligatory 100nF caps at each chip right across the supply pins and at the input and output of 7805. "

I don't understand this one ...

"Increase the pull-ups from 1k to 4k7...10k. "

I can do this

"The RC-reset at µC is highly disadvantageous. Use a proper reset chip to provide a true power-on reset and brown-out detection. I like to use the MAX1232 and its built-in watchdog, like shown in this example here: "

I'm all up to better ideas. What is the advantage of using your circuit?
I've been using this RC method in many of my circuits before ... Fortunately they are working fine up until now.

"Have the crystal oscillator components shortest connections, like shown in this example? "

I have done that.
One question after seeing your PCB ... What are pin "3" and "4" of the crystal used for ( My crystal only has 2 pins ) ? And what are they connected to ( Ground )?