I'm not badly stuck for space. Price isn't the biggest obstacle, but it's always good to keep costs down.
I'll need the same basic board design to handle 24V, 48V and -48V supplies, either directly plugged in or through PoE. I might also need a 12V version. Rather than re-design the entire circuit around the different PSU requirements, I've designed it with a "daughterboard" arrangement. The individual daughterboards take whatever supply voltage they're designed for, and output +5VDC to power the mainboard as well as an output scaled in the 0-5V range to represent the actual supply voltage (the whole point of this circuit is to monitor the parameters of the power supply).
The daughterboard is 1.2" by 0.9", so there's a little room to play with. The input and output supply pins are arranged at 0.1" spacing so I'll be able to mock up daughterboards on stripboard and test various components before committing to a PCB layout.
As for power consumption, I'll be driving an Atmega328 and a W5100 with a number of fairly low brightness SMT LEDs and (optionally) a 16x2 LCD without backlight. I think I'd rather have the headroom of a full amp available.