No. Not ever.
Why? Well, which reason should I give first?
(1) Editors aren't "site suggestion processors". They're "category builders". If someone is working in category X, they're looking for sites in category X. If they find a site in category Y, what'll they do?
--Most likely, ignore it. It's not relevant at the moment.
--Next most likely, just move it to category Y. Where, after whatever delay in category X, it can start waiting for review by an editor interested in category Y.
--It's always possible that the suggestion will just be deleted, especially if it has been looked at before.
None of those things are harmful, but none of those are what anyone would want to go out of their way to get nothing better than.
(2) The "last date modified" is no real guide to the amount of activity in a category. Some categories (this is not just a theoretical example) are reviewed almost daily but since so few sites actually get listed except in subcategories, they may appear ignored. Other categories may have been ignored EXCEPT for some flying visit by an editall to fix broken links, misspelled words, etc.
For all you can really know, you could be skipping an actively reviewed category to drop your suggestion into a dormant one.
(3) Assuming (which you can't) that you really know the last activity in a category, you still don't know the NEXT activity. A new editor might join, a group of editors organize a group-cleanup, a formerly-active editor move away, ... and again, you could miss out by trying to "game the system".
(4) Aside from all practical considerations, there's the ethical issue: do you really want to be the kind of person who deliberately helps other people LESS in order to get QUICKER help for himself? That way leads to soul-rot and putrified reputation, no matter how successful it seems at the moment.
.