Remember it's the contract (service requested), that will dictate the level of traffic information or deconfliction advise given
This "contract" business is actually a fallacy - as anybody flying for real will know.
You can be under a traffic service but the controller is under no obligation to pass you details of any traffic whatsoever, if he is busy. I have had many encounters with such unreported traffic.
Some legal tw*t in the UK regulatory apparatus came up with this "contract" idea, but what has happened is that pilots are told they must comply with it, but ATC does not have to comply, and if they are busy they obviously cannot so why the hell use the word "contract" when no contract can be possibly entered into because one party (at least) is physically incapable of complying with it
ATC is there to help you to the best of their ability but to call it a "contract" is plain bizzare. An ATCO providing
radar vectoring is responsible for your obstacle clearance but that is about as far as legally enforceable ATC liability goes. Everything else is subject to controller workload, etc.
Enroute, I go for a radar service only, with a listening watch the rest of the time.
Not whether you are IFR or VFR
True but there is ample evidence that ATC are likely to offer a better service (or any service at all) to a pilot who comes across as knowing what he is doing.
And navigating via IFR waypoints, or flying outright IFR at some "high for normal GA" level (e.g. FL040) helps to get ATC to work with you. Whereas if you turn up flying towards some piece of CAS and describe your route in terms of half a dozen village names (which only the locals will know) and flying VFR at 1400ft, the Class D owner is more likely to refuse a transit. Especially if you have wasted a lot of his time by stuttering on the radio, giving your whole inside leg measurement
It is only human nature.