Here are a few ideas for spending time in Hoi An:

Old buildings: With Hoi An's unique tourist ticket system, you get to see 5 attractions. The assembly halls (temples) are only mildly interesting, but the old merchant houses are well worth a visit.  

Japanese tombs: These are in a rice field located between the edge of town and the vegetable village. Not a lot to see but a pleasant spot to visit and good for a few photos. Be forwarned -- there is an old farmer lurking there who claims to own the entire field. If you let him, he will "show" you around and pose for photos, and then ask for money. If you do pay the old rogue, make sure it is only a token amount. The best way to get there is to rent a motorscooter or a bicycle. The traffic is pretty slow in Hoi An so that is not as suicidal as it sounds!  

Sugarcane juice beside the river: Don't spend all your time in the fancy restaurants. Take a seat with in the locals in one of the outdoor "cafes" beside the river and have a glass of freshly squeezed (more like crushed?) sugarcane juice. Best value in Hoi An.