In reply to helix: its been said already but Sennen is your best bet, especially from st ives. The rock is about as good as it gets, the acess is easy with or without an ab and the routes are interesting and varied despite being quite short.
TRewavas is a good crag but not a sea cliff really (i.e you can see the sea but you a a fair distance above it). plus from st ives its a lot further when sennen is just up the road.
Bosi is great, well above the sea but still very full of the sea cliff atmosphere. Easy access in by foot at the west end plus a number of easy scrambles into various other points of the crag. Awsome longer routes with a few shorter gems at either end.
There are lots of others, as you say, and to pick the best of the rest is hard. The guide is pretty accurate in pointing out the looser, more friable areas; avoid these and you will be fine.