The core devs have discussed this topic for years. Hopefully, XT will push them to action. If not, we will just opt them out.
A higher capacity system will be a lot more expensive to spam. I can't help you, if you don't understand this.
If valid transactions are something like 1.1mb and the free space is another 6.9mb, there is high risk of including several megabytes of transaction spam per block, with very low or even zero fees. It will become expensive only if an attacker tries to fill the entire 8mb block, otherwise his average cost per megabyte of spam will be cheaper.