I think it depends on what my goal is for the town. For my main town, I have a more completionist attitude, but even then I don't feel like I need to redo everything on my alt. My alt is mainly there for aesthetic purposes, so I don't feel like investing the time to work on his badges, encyclopedia, etc.
I will feel like my main town is 'done' when I've finished all of the following things (although I'll continue to want to play it and enjoy my villagers and the fruits of my labor):
- Fully completed Main Street (Done)
- Fully completed Museum (Done)
- Fully completed encyclopedia on my mayor (Done)
- Collect all badges on my mayor (WIP)
- Unlock all emotions from Dr. Shrunk on all characters (Done)
- Expand each character's house to my desired level and pay off all associated loans (Done)
- Finish decorating each character's house (Done)
- Finish landscaping my entire town, including placing and paying off all PWPs that I want (Done)
- Finish decorating the rooms on the upper level of the Museum (Done)
- Obtain all of the Fortune Cookie items (Done)
- Complete Puzzle League and Desert Island Escape with my mayor, including obtaining all special items (Done)
- Obtain all of the golden tools on my mayor (Done)
- Obtain and maintain Perfect Town Status for as long as possible, but if my desired landscaping affects the status I'll let it drop (Done)
I don't care about completing my catalog beyond what's needed for the badge. I don't have a full set of dreamies and will contine to cycle through villagers, so obtaining dreamies isn't a goal for me. I will continue to work on obtaining my villager's pictures, but since they will continue to rotate that task will never be complete. There are certain events I will always participate in, but some I don't like and don't care for the rewards so I skip them.
That's for my main town, but if I make an additional themed town, I think my focus will mainly be on the aesthetics. I would probably consider that town complete after I got the landscaping, characters, villagers, and houses to all look exactly the way I wanted.