Ok, some new research data about "problem":

output=overlay still result in segmentation fail, no matter of settings. ho ever, I "discovered", that error lines just before segfault - about alsa, snd etc - are not related to problem. They appear also, when using output=surface.

It seems now, that surface is only one working mode for N900. Ho ever, it's possible to use it with image stretched to full screen - using <any scaner>2x (3x ones result in segfault, probably for resolution reasons). It seems ok - still I think surface=overlay with scaler=none and fullscreen resolution set to 800x480 could be faster, but it isn't working. And, I'm not sure about any speed advantage, it's just guesswork (hardware scaling).

It seems that I might be mistaken - maybe it was surface, that worked month or two ago. It's possible that I experimented, and by accident, left output=overlay for a long time, resulting in "me thinking" that such settings worked before.