Both Sruti and smrutis constitute valid pramANas. We have to keep in view that smrutis have only Sruti as the base. Though there were many SAkhAs (recensions) of the Vedas in the days of yonder, only a few are available now due to various reasons.
anantA vai vedAh ! ---- TaittirIya KAthaka
The Vedas are infinite. Thus while a particular aspect (for example, mandatory performance of trikAla sandhyA including mAdhyAnikam) specifically covered in the smrutis could have been based on a Vedic statement which was existing in a particular Vedic recension at that point of time but not now, it may not be correct for us to conclude that the particular aspect is not backed by Vedas. Hence it would be very difficult to overlook what is stated in the smrutis as being something which is not mentioned in the Vedas and hence need not be followed.
One cannot properly understand the intended and intrinsic meaning of Vedas. As Vedas are complex and innumerable, the Rishis through their great tapas composed the Smrutis which define what is dharma for a particular Yuga.
In order to understand the Sruti in the proper perspective, one requires the guidance of smruti. Interpreting the original Vedic Mantras on our own accord is dangerous in the modern environment.
For each Mantra, there is a Rishi, a Chandas and the devatA. One cannot overlook the Rishi and chant any Mantra including GAyatrI MahA Mantra. As Rishis are the Seers of Vedic Mantras and the authors of smrutis, we hold them in high esteem. Rishi TarpaNam is offered to them. KAnda Rishi TarpaNam is also there. All the Srauta, grihya and smArta PrayogAs are done even today based on the statements of great Rishis like Apastamba, BodhAyana, ASvalAya, Jaimini, LAtyAyana, KAtyAyana and so on. In addition, we have sanakAdi Rishis, Sapta Rishis , NArada, BharadvAja, Veda VyAsa and so many others.
Each BrAhmaNa (however materially he may be rich) is born only as a debtor with triple debts. He is indebted to the Rishis, DevAs and Pitrus. The Rishi debt is discharged through brahmacarya, Deva debt through performance of yajnas and Pitru debt through progeny.
JAyamAno ha vai brAhmaNah tribhir rNa vA jAyate !
brahmacaryena rishibhyah !
The Rishis including Rishi Patnis are to be respectfully worshipped. Without them, the Vedas would have disappeared. The smrutis, which are Rishi Proktam are therefore equally valid like Sruti.
namah parama Rishibhyo namah parama Rishibhyah !
Whatever one feels like doing according to his mental make-up does not constitute dharma. That is why in Bhagavad GItA , BhagavAn advises all to follow dharma as ordained in the Scriptures :
tasmacchAstram pramAnam te karYAkArya vyavasthitau!
jnAtvA SAstra vidhinoktam karma kartum ihArhasi !!
-----Bhagavad gItA ! 16.24
One who does not follow SAstras gains not Sukham or Siddhi or parama gati.
yah Sastra vidhim utsrijya vartate KAma kAratah !
na sa siddhim avApnoti na sukham na parAm gatim !!
---Bhagavad gItA 16.23
Learned sees through the eye of SAstras
" ----kavibhih SAstra cakshushA ---"
---- SrImad BhAgavatam x-84-36
Sruti smruti mamaivAjnA yad tad ullanghya vartate !
AjnAcchedhe mama drOhi mat bhaktOpi na vaishNava !!
vedamUlAh smrutayah !
durbodhA vaidikASSabdAh prakIrNatvacca ye khilAh !
tatraita eva drushtArthAh smruti tantrai pratishthitAh !!
Srutim paSyanti munayah smaranti ca tathA smrutim !
tasmAt pramANamubhayam pramANaih pramitam bhuvi !!
According to Angiras, those who are learned in pramANas should duly take care of them. Otherwise, authentic pramANas would get destroyed by baseless pramANas.
pramANAni pramANajnaih paripAlyAni yatnatah !
sIdanti pramANAni pramANairavyavasthitaih !!