If I were the Phin's owner and had an extra billion laying around
here is what I would do:
1. Make the stadium more comfortable for the fans. Put air conditoning under ever seat and mist machines like they have at a lot of outdoor bars/restaurants. I don't think a roof is necessary but maybe shade most of the seating area and just leave the area over the field in the sun. Here is a link to Allianz stadium in Munich, Germany. I think they spent around $500 Million to build it and it seats about 65-70,000, and the fans are close to the field. We need a stadium like this.
http://images.businessweek.com/ss/06/06/worldcup_arena/image/allianz_arena1.jpg
2.
Don't force people to pay $20 to park their car. I go to Air Force football games....parking is free....everybody shows up to tailgate, and it is a great time. With the economy the way it is, don't keep people away from games by overcharging for parking.
3. Build areas around the stadium that people want to go....like shopping malls, restaurants, bars, etc. When I look at Landshark Stadium it looks like it is in the middle of a swamp.
4. WIN and the fans will come.