IMO, the woodwork on the old basses is just as good as the new ones, having owned a '75 Series I. However, the old electronics are noisier, and the revised bridge that turned up in 1977 or so was a major, major improvement over the original channel design. In those regards, the newer basses are much better, and to me, would make finding a newer Alembic worth it were I to buy another one.
The 70's basses do have an undeniable character, however, and there may be some worth associated with that intangible.