Depends if you feel the safety is gap is best filled with you being aware or others being aware of you. With a PCAS setup you don't need a transponder so you deal with significant amount of the first former. By fitting a transponder you deal with a minority of the latter.
If anything, without a transponder you don't suffer the nuisance alerts that I mentioned earlier.
I strongly disagree with the above. Carrying a Mode C/S transponder means that
radar equipped ATC can see you and see your altitude. This enables them to deliver a meaningful radar information service (RIS) to all participating traffic! Anybody flying under an RIS (which is great many pilots; an RIS is worth having at any time) will know how hopelessly useless the service is when other traffic is non transponding. You just get loads of reports of "level unknown" traffic which most of the time will be somebody crawling down ~ 1000ft but you cannot bet on it. In turn, the large traffic reporting workload this creates for the ATCO means that traffic which might actually affect the recipient of the RIS may not be reported.
Carrying a Mode C/S transponder also makes you visible to commercial traffic's TCAS systems which (should you make a navigation error and end up busting CAS) can then take avoiding action. Of course, none of the people who don't carry transponders ever make a navigation error so they can ignore this paragraph
Carrying a Mode C/S transponder also makes it easier to get CAS transits in many areas, especially abroad.
And finally carrying a Mode C/S transponder makes you visible to
GA traffic carrying some kind of traffic warning device, either one of the cheapo transponder receivers, or the full £20k system.
It is obvious from the pattern of UK GA that pilots who fly without a transponder are statistically much more likely to be flying low down, and it is low down where they are much more likely to get hit. So the "only bimbling" anti-transponder argument is the wrong way round. These are the very people who have the biggest benefit from carrying one.