I recently swapped out the stock 2.73 gear in my 1990 305 Formula with a 3.42 that was given to me. Would there be enough difference to merit the expense of going to a 3.73? Thank you for your help.

Unless you're running a real large cam, NO. You won't see much of a difference in those gears. I just put in a set of 342s while I'm rebuilding my other 10 bolt. I can't tell much difference except in town at 30 mph.