Thanks to all for the detailed replies. I just wanted to let everyone
know -- for future google searches as much as anything else -- that
dumping the database, upgrading to 7.4.1 and reloading did solve the
problem. All the queries I mentioned now use the available indices,
except for understandable cases such as the number of rows in a table
being really small.
Thanks for the tip and thanks for the improvements in 7.4.1 that fixed
this problem.
steve