I have a small share in a company which is selling land for single
family homes.  The total acreage is 100 acres.  The lots will be
divided into "cluster" homes (about forty acres) and upscale half-acre
lots for the rest.  This land is in a desireable location.  It has
been  improved w infrastructure and amenities.  I'd like to know how
much it's worth.  An adjoining property was recently sold (unimproved)
for $90,000 an acre.  Is this enough information to estimate an
approximate value of the land?

You could see what information Zillow.com shows for the area.

Try it, might want to think about selling your own house.

Why don't you ask the company that owns the land what they consider
what it is worth? They are in the land business, they probably know
the market and what they are expecting the lots to sell for.