Excuse my ignorance......................
Presumably TCAS relies on other aircraft being txpdr equipped - and that the txpdr is switched on?
There are approximately 8 regularly flying aircraft in our barn and at the Club I am a member of at least another 60-70. None have transponders. Because they are microlights and 'cheap' to opearte they are regularly flying.
Is there any chance at all that TCAS could make you complacent?
Just a thought