The more advanced "more" searches should have both before and after dates as well as the possibility of date ranges (two pop-up calendars).
Additionally, it would be great to be able to set search options of various types including:
1. quick search (standard box) admin setting for relevance as opposed to date being standard.
2. permissions to allow moderators, for example, to get ALL results in search or at least more than the stock 200 or 300.
Basically, I think the entire search must be looked at in terms of both admin and user options - these improvements should be easy from a programming perspective and yet will add much flexibility to the system.