In any case your experience doesn't match mine. On a machine with a sizable raid controller setting random_page_cost higher does generate, as expected, plans with more bitmap heap scans which are in fact faster.
We're running postgres backed by a NetApp 3020 via fiber and have had a lot of success setting random page cost very high (10). Sequential reads are just that much faster. I'm not sure if thats because we've configured something wrong or what, but thats a really useful knob for us.