It would help I'd think, yes.
I think it's important to consider the administrative nuances as well - for the purposes of this discussion we're focusing on unsigned routes which are part of an existing system TM already has, not a separate system that TM does not already have.
Take New York for example. New York has an administrative distinction between "Touring Routes" (numbered 1-899) and "Reference Routes" (numbered 900-999 with letter suffixes).
Touring Routes are intended for navigational use by the motoring public, and are all signed (possibly except NY 495, which is only erroneously signed as I-495... but details). Reference Routes, on the other hand, are not intended for navigational use by the motoring public, and with only a few occasional weird exceptions (which are usually errors) are never signed except on reference markers. Since it is clearly a separate system, I do not advocate going and including NY reference routes.
On the other hand, across the river in New Jersey, the situation more resembles Oregon's - there is only one state highway system, with no administrative distinction between signed and unsigned routes. The handful of NJ state routes that are unsigned are not by any broad policy explicitly supposed to be unsigned - they simply are not signed because the state has never bothered putting shields up, and for any given route this could change on the whim of a DOT engineer without any established rules being broken. These are the sorts of routes that we'd want to consider adding.
In cases like this I'd be fine with making "New Jersey Unsigned State Highways" (usanju) a separate system so that users who don't care about unsigned highways can continue ignoring them, but this would be a distinction we're creating - the state does not consider them to be a separate system.
