What is there left to do in your current town? Pluck the weeds, maybe? Make more money for random public works to make you feel like you're progressing when you've already gotten far (I assume anyway)?
Restarting your game gives you goals, albeit they're goals you already accomplished, I once again assume it's been awhile since you've played so they aren't fresh in your mind.
Designing towns is so much fun and you'll get to create a new and exciting town, or simply improve on your old town theme, in case you didn't something weird you didn't like very much.
There will be much more to do, and it'll be a lot more fun than continuing a near end game town