The latest version of NodeMCU firmware (8/9 Jan 2015) is way better in providing more free heap at startup. Now it starts up with around 19/20K instead of around 15/16K.
But unfortunately it seems far more unstable than the previous versions regarding usage, and as a consequence it reboots more often:
Before the end of 8th of January, heap usage decreased as time went by and had at the end a reboot.
Because I only own at the moment a single esp-01 board, I can’t keep track of NodeMcu heap management improvements, and moved out building things with the native SDK.
I’ll try this firmware again when some improvements are made.