I could be wrong about this--it's entirely based on personal speculation--but I wonder if the capacity is more of a concern in Manchester, which has to compete in essentially the same market as arenas in Boston, Lowell and other nearby cities. Portland and Manchester are different cities, but Portland in general seems to be a bit more self-sufficient than Manchester, which is in sort of a grey area between an independent city and a satellite of Boston. My assumption would be that this goes for Portland, as well. It's a much longer drive or train ride from Portland to Boston than it is from Manchester to Boston, or even Lowell. While a bigger arena probably wouldn't hurt--and while I think it would do a ton of good in Bayside--I wonder if 8,000 seats in Portland is just as good as 10,000 or whatever it is in Manchester.
As for the architecture, the renovation looks like it will do a good job of adding some energy and interest along the street. That's something that is lacking at the current arena, as well as at the Verizon in Manchester, in my opinion. While I like the look of the Verizon from afar and the entrance plaza and glass wall are great during an event, it is far too blank along Lake Ave and the setbacks create a weird dead zone along the sides. Pushing it up to the street and adding retail or something along street level, as well as getting rid of that electronic sign at the intersection, would have made it much more urban I think. Especially after the renovations, CCCC should be much more urban-appropriate and interesting from the street than the Verizon, in my opinion.