I must say, your post is by far one of the best "give me guidance" questions ever. Most just say, I like small towns, anyone have recommendations? THANKS for all the info. It seems like you have a "go where my travels take me" attitude which is fantastic, the BEST way to travel if you can do it.
Based on your many thoughtful answers, I would suggest rambling around the upper midwest, MN, WI, MI, IA. OH. You can definitely get a lot of small town feel without getting too much dead small town feel. There are LOTS of bike paths/rail trails, CGs, bakeries, etc. and enough historic/cultural aspects to keep you happy. There are several areas that have a heavily "foreign" influence, i.e. the town has a high percentage of the population with a Norwegian, German, Amish, etc. ancestry.
Be sure to search each state for "bike maps". For instance, IA has a great bike map:
https://iowadot.gov/maps/digital-maps/state-maps/iowa-bicycle-map.
The other states do also. Based on your post, you seem to fairly experienced at touring. In case you don't know, shoot for traffic counts that are less than 2k a day, ideally less than 1k vehicles a day. If traffic is high, look for shoulders.
I would probably start in Iowa, ride north into Minnesota, dip SE to central Wisconsin and their numerous rail trails, ride up to Door County, WI, swing south to Manitowoc and take the ferry over to Michigan before heading south to Indiana and Ohio.
I would encourage you to review a lot of USA Today's "best of" travel articles. They have numerous "best of " bakeries, ice cream, museums, odd attractions, etc. for all 50 states. Granted they can be hit and miss as far as the "best" but it gives you at least some stuff to consider. Make a list of all the things that interest you and if you get into the area, ride to it.
Enjoy the ride! John