DOWNSIDES
One 'downside' I see is the advanced planning, configuration and troubleshooting efforts required for LACP bonded interfaces. Another 'downside' is the perceived redundancy resulting from bonded interfaces, redundant PSUs, hard disk RAID.., while it's still only one chassis meaning no physical redundancy (separate racks, rooms), no harddisk dd dumps, no instant fallback solutions, limitations on redundant hard disks and PSU's that are only available on expensive high-end Smart-1 Appliances (225, 3050, 3150), and so on.
VIRTUALIZATION
I prefer running the SmartCenter as a VM host within VMware ESXi instead of maintaining a physical appliance. This allows for easy VM snapshots and reverts making it easy and safe to quickly test a new hotfix, migration, whatever.
MANAGEMENT HIGH AVAILABILITY
In cases where a physical management appliance has to meet advanced redundancy requirements, I recommend adding a secondary management appliance to get a real Management-HA solution.