People talk about term limits for politicians, but what I'd like to see is term limits for laws.

Requiring (most) laws to sunset if not passed again sounds like a brilliant idea, and I'm not sure there are any arguments against it beyond "it would just cause more gridlock in congress" (which I would generally consider to be a good thing) or "people would work around it so it'd be moot", but if there are I would love to see them.

there would be giant omnibus bills that reupped everything

The workaround to this (and other issues) is to ban bills greater than a certain length, and/or actually require the contents to be read by/in the presence of every congress critter before a vote (rather than allowing congress to waive those requirements.)