The small ancient Greek denominations like the hemi-drachm and the obol are underrated. Most collectors prefer the bigger pieces like the tetradrachm and the stater. This is unfair.
As far as the artistic quality is concerned, small coins are not inferior to their bigger counterparts. The images are mostly as fine, if not finer, as on the bigger pieces. The technique neccessary to produce these coins, the cutting of the die as well as the striking of the coins themselves, was, due to their size, more difficult than with the bigger coins.
As regards to the price, the smaller denominations often cost only a fraction of their bigger counterparts. A collector can still get bargains here.
Nowadays small coins are much easier to admire due to technical advance. The possibilities offered by digital photography and the computer are endless. There is even a digital microscope for coins available. The craftmanship and quality of these little masterpieces finally come into their own with these tools.
There is no reason I can think of why collectors should not include small ancient Greek denominations in their collections.