What you are doing is to provide a semi-isolated power supply for the uC. This is not a bad idea; however it would be much better to provide enough power to keep the input from dropping below the required voltage when the relay is on. An even better way would be have a separate power supply for the electro-mechanical devices and a separate power supply for the electronics, I have always used that approach when electro-mechanical devices were involved.

The resistor in series with the power is dangerous, it makes the Vcc dependent on the load current. While this might work in setups with a somewhat constant current consumption, someday someone is going to add something and wonder what happened since an uneven load will create random problems.

Provide enough power to keep the input to the regulator high enough at all times and use a big cap to smoothe out the spikes.

Have fun,

Erik