"...several scripts which it would seem wise to turn into modules... read a file into one or more hashes, manipulate the data and write the file back...am I overengineering this...?"

One of my first posts on PM was about something similar - less or more: The Way I Moo

To be honest: i gave up this concept (in this case) and switched back to plain old modules.

And worse: From time to time i put the stuff (my subs) in one file (the script), even if i repeat myself ;-)

Best regards, Karl

P.S.: About the basic theme (overengineering...): IMHO yes.