  In the distant past, telescopes were known, first and foremost, for the sizes
of their apertures. Advances in technology are now enabling astronomers to
build extremely powerful instruments to the extent that instruments have now
achieved importance comparable or even exceeding the usual importance accorded
to the apertures of the telescopes. However, the cost of successive generations
of instruments has risen at a rate noticeably above that of the rate of
inflation. Here, given the vast sums of money now being expended on optical
telescopes and their instrumentation, I argue that astronomers must undertake
"cost-benefit" analysis for future planning. I use the scientific output of the
first two decades of the W. M. Keck Observatory as a laboratory for this
purpose. I find, in the absence of upgrades, that the time to reach peak paper
production for an instrument is about six years. The prime lifetime of
instruments (sans upgrades), as measured by citations returns, is about a
decade. Well thought out and timely upgrades increase and sometimes even double
the useful lifetime. I investigate how well instrument builders are rewarded. I
find acknowledgements ranging from almost 100% to as low as 60%. Next, given
the increasing cost of operating optical telescopes, the management of existing
observatories continue to seek new partnerships. This naturally raises the
question "What is the cost of a single night of telescope time". I provide a
rational basis to compute this quantity. I then end the paper with some
thoughts on the future of large ground-based optical telescopes, bearing in
mind the explosion of synoptic precision photometric, astrometric and imaging
surveys across the electromagnetic spectrum, the increasing cost of
instrumentation and the rise of mega instruments.
