A typical setup for HA would be 2 aggregator nodes and 2 leaf nodes. You can allocate the memory however you want. For example, you could give 32GB to all 4. Or give 16GB to each aggregator and 48GB to each leaf. (I'm a MemSQL Product Manager by the way.)

Do you have recommendations on provisioning memory in aggregators vs leaves? That is, would one of those configurations make for sense than the other for typical workloads?

In general more memory should go to the leaves. All data is stored there and MemSQL will push processing to the leaves whenever possible.