One - the atmosphere can't get much better - the additional SRO and Leftfield GA add as much or more atmosphere as would 200 to 500 in temporary bleachers as evidenced by last years conference tournament and regional
Two - there is no way to economically add temporary bleachers that meet fire marshal standards and give you the same amount revenue as the SRO/Leftfield GA tickets do
It would probably cost $15k to $20k to bring in temporary bleachers for an additional 200-300 fans - how many games would those actually be sold? priced? (be hard pressed to sale them more than $10 a seat) and you would still have the costs associated with vending and toilet facilities...
$10 SRO and Leftfield GA tickets are the way to go - same atmosphere and more revenue