If things are consuming more memory over time, personally I would look into what and why that is happening. Ideally you want to have things that consume relatively stable amounts of resources on the whole. If they spike or, of more concern, if they increase over time, then more resources are only going to lengthen the time you can run the hub without rebooting. The key word here is ideally.... I'm not suggesting I have reached this state, or have some magic solution to achieve it, only to say that throwing more resources in the mix is unlikely to change things in the long-run, IMHO.
This from the guy running 4-5 HE's for similar reasons to what you are raising .... Granted more resources may make some things run faster, therefore reducing the bottlenecks that may occur, but the improvement may be hard to quantify on a user-by-user basis, it would depend quite heavily on what Apps / Devices you use, so justifying the expense would be hard to quantify, just because you have a "slow" system would not necessarily mean you would benefit from the rolls-royce version...
There are also various reasons why people may need or want multiple hubs, including splitting functions like I have between lighting control, general rules and cloud-related stuff. I like the ability to have my lighting not impacted by any outage to the rules or cloud HE hub, as much as that is a rare event. Separate to my own circumstances, other may have other reasons to run multiple hubs, so it feels like the complexities people experience in running this setup may be worth exploring and refining, rather than outlaying additional expense in developing and releasing another version of the hub. What kinds of things do you find complex to manage?
I'm not against a beefier hub or enhanced version with extra features, just want it to be something that can be easy as to explain to situations where users will benefit from outlaying the extra $$.