Even now, the XL Center is not a bad place to watch hockey or basketball. The long standing problems are operating costs that makes it expensive to operate. Basic stuff like utilities, lighting, heat, air conditioning, plumping, pest control, and costs associated with maintenance like cleaning and inspections, plus human costs like staffing, security, how efficient are the concessions and merch, then, as always, insurance costs.
The point is, that's the important stuff. Little of it has a major affect on visitor enjoyment of an event. The XL has nice sight lines and information signage. But it could use some boxes and such to make it more profitable for the sponsors of an events. That would help XL to draw more attractions to the venue.