Buff the Nexus
I think that the Nexus should receive some buffs. It has 5500 health, 0 armor/magic resistance, and 25 health regen per 5.
Some more health and/or scaling armor would make it a little less pathetic. Something like 5 armor per minute would be enough (even if you want to start the scaling at a point other than the beginning, such as the 15-20 minute mark, although you'd need more armor per minute to compensate).
Thoughts?