Question
I live in Ontario Canada and have a Locus tree that is about 30 yrs. old. Some of it's branches are now dead and it is quite sparce in foliage.
Will pruning off the dead limbs help extend it's life and increase it's foliage.  

Answer
FOLLOW-UP
I didn't answer you main question (sorry!), which was should you prune it to increase its foliage & survival.

Answer - It is worth a try.  It is a vigorous tree, and a dead branch will only look bad.  Plus it looks poor to have dead, hanging branches and there may be other disease issues that a competent local arborist can assist you with.

-Marc

* * * * * *
I have just enough knowledge about trees to be dangerous!  However, I know that Locus are susceptible to leaf & branch dieback when young.  When they get older, I don't know much more, other than it抯 an East coast native.  It is a tough tree, able to resist desert conditions, like mine.  

Locust is NOT tolerant of shade, but I think if you have a 30-year old specimen, its safe to say the branch shade is not the problem (lower limbs die back in excessive shade).  If it has a thick head, maybe it抯 the upper branches shading the lower branches?  Still, this doesn't sound like your problem.

My advice would be to talk to a competent local arborist, familiar with your area and invasive pests that may also be causing this problem.

Their website is: http://www.isa-arbor.com/

Good luck!!
-Marc