Normally I maximize the use of instances, given that all the instances of the object in question logically have the same scope or function as far as events go.
However, if using all separate objects works and makes it easier for you, there is no reason not to unless you can actively notice or measure a performance difference.
I don't think 100 objects would have any measurable impact on performance. On the other hand, slider bars objects are html form elements and those don't always play by the rules. Anyways I wouldn't bother worrying about performance.
I'd go crazy building events for 100 separate objects if I could do it just for one instead though. Then again, you've got families to make up for that as well. This engine gives you a lot of flexibility to work in whatever way you feel most comfortable.