It is hard to say if it's worth fixing or not because you give no info
about the car other than the year and the problems you are having
with it. What condition is the body in, the interior, how many miles on
it, how well did it appear to be maintained etc.?
As to what makes starters fail, it could be any number of things. More
than likely the first one failed due to normal wear and tear, and the
second one could have failed due to a fault internally during
production. Was the second one factory new or rebuilt? Over the
years I have purchased many parts like starters, carburetors and
brake calipers both New and Used, that either didn't work when
installed or failed shortly after. There are 2 schools of though on
replacement parts. One is factory new is better. The other is Rebuilt is
better. I personally have had better success with rebuilt parts, but the
secret to that is they must be COMPLETELY rebuilt, not just tested
and certain parts replaced.
As to your low beams and tail lights not working, did they work when
you purchased the car or not? Have you checked all the fuses and
relays? The smoking under the hood, it could have been a loose wire
or connection, or a small strand of wire or metal filings that were there
from some work and shorted things out, or there may have been some
wiring work or accessories added at sometime during the cars life that
wasn't done properly leaving a connection loose or crossed.