To prevent queue overload there is already in place a cap on the queue size (although, I'm not sure what this is) and the restriction that anonymous users cannot touch brand new posts (source: FAQ).
Remember that 2K users can edit without suggesting, and until recently this was the only way for users to edit. As such, all the suggested edits are a bonus to us, from those without the direct privilege to edit wanting to help, and these are mostly valuable. We don't want to discourage too many of these, otherwise what's the point in having the suggested edits mechanism?
Statistics on the rep ranges of users making these suggested edits would be most useful; to determine if a rep requirement would be effective or not, and how many edits it will deflect.
I'm personally of the opinion that the current setup is sufficient, although I realise that the SO experiences a much higher volume of these things (well everything) than other sites on the network.
However, in case a change is deemed necessary, can I offer an alternative solution: lower the rep boundary for people gain access to the
/review tool that lets them access the suggested edit queue, increasing the number of approvers instead of decreasing the number of editors.