Tower squatters should be auto logged off after 20 minutes especially during the day. Anyone who is afk longer than that is interferring with people who want to get in the arena and actually play. 20 minutes is more than enough time to make a head call, grab a beer and make a sandwich.
The complaints about arena caps could probably be lessened by using percentages, changing the initial caps and a making a few other changes. This would only be for when the cap system kicks in. Set pink to an initial cap of 200 since it has a tendency to fill up first and blue to an initial cap of 75. Using something like 75% capacity in blue as the initial line to increase the cap in pink, once blue gets to 75% capacity increase the capacity in blue by 50. If pink is full and blue jumps to 90% capacity the caps in both arenas jumps by 50 and the caps remain until blue once again reaches 75% capacity then increase the cap on pink again by 50 spots, then rinse and repeat. Of course blue would need to be running a small map during this time period.
That's just based on the assumption that percentages aren't being used now to adjust arena caps, and there will still be people not being able to get in to pink when they want to but it could be fewer instances.