It’s a bit old topic, but maybe I can add some comment here rather than opening a new one.
I have checked the “multiple search field” box which provide nice options, but maybe a few ones are missing (In my very humble opinion)
I was formerly a gmail user (nobody’s perfect) and they had a feature I found pretty interesting.
They offer to use some keywords to refine search.
The ones I liked most was: “has:attachement” / “has attachement pdf”…
Very powerfull when you look for a specific attached file (can be combined with other criteria).
An other one was search on size: “larger_than:5M”
Very powerfull when a bit of cleanup is needed (or combined if you look for a specific PDF larger than…etc).
They have other keyword like “from:” or “to:” etc…
I like the keyword idea in the search field (a bit “geek”, a bit less clicks, only typing). But additional fields in the advanced search could do the job too (or both? )