Could you clarify - and I believe this is Sönam's point - how sadhanas and a load of practices relate to the following:
"Mahamudra and Dzogchen training means not fabricating anything, just allowing the continuity of our natural state. This is not our habit. We must train in developing a new habit, but this practice is not meditation, but familiarization. When we finally arrive at the dharmakaya throne of nonmeditation, there is nothing more to cultivate; there is not even an atom to meditate upon, and yet we are not distracted for even an instant. We need to train in this. It is also phrased as mental nondoing. ... In the guidance manuals for meditation, it is often phrased like this: Do not alter your present fresh wakefulness. Do not rearrange even as much as a hair tip. Just leave it exaclty as it is."
(Choky Nyima Rinpoche: "Familiarization" in Quintessential Dzogchen, p. 199)
Nice of you to provide a quote by my root Guru, it makes it easier to respond
First "the natural state" is something that we have to discover, or recognize. Until we done that all practices we do, either with or without form, whatever we call them is a little superficial and conceptual and completely dependent on thought and mind. Your practice is to try to accumulate enough merit and wisdom to receive direct introduction and recognize the natural state.
After recognizing the natural state you realize all practices you do are aimed at stabilizing this recognition. So while practicing your Yidam it is very possible to just allow the continuity of the natural state. Of course if try to push it, it becomes fabricated so instead you just allow it to last as long as it does. The essence of the Yidam is the natural state so you are not drifting from your development stage. I feel a little strange trying to explain these things, you should read the books of Tulku Urgyen if you want to understand it better. Also both compassion and devotion are two powerful enhancement for the natural state. This is why Guru yoga is so important in Dzogchen. However, in general all practices are designed to empower your wisdom (at this point the natural state), compassion and devotion. So in no way do they impede the natural state. This is also why I doubt practicing "only" the natural state. You will force it and end up fabricate it.
"The direct, hard to understand, subtle field of knowing, the Great Path, is non-conceptual (akalpana), and entirely beyond the grasp of intellectual thought. Divorced from verbal ideation, it is difficult to point out and as difficult to enquire into. It cannot be communicated through words and [therefore] is not within the scope of the neophyte (adikarmika). Nevertheless the path is to be approached through studying scriptures (sutra) of the World-Teacher and following the personal instructions (upadesa) of one's Guru-ji."
Bodhicittabhavana by Acarya Sri Manjusrimitra