Interesting, I just found this post on facebook, which talks about SP's opinion on sanayasa.
In spite of his childhood disgust with most sannyasis, we know that Srila Prabhupada recognized Bhaktisiddhanta Saraswati as a bona fide spiritual authority. One might think that from this point forward, he accepted the necessity of the sannyasa asrama. However, in 1949, about ten years after the passing of his spiritual master, and after witnessing the strife in the Gaudiya Math created by his materialistic Godbrothers, Srila Prabhupada again voiced his disapproval of the sannyasa asrama (though, significantly, not the brahminical class) as he formulated a proposal for the creation of an ideal spiritual community:
>> ...The Gita-nagari, by its cultural propaganda and otherwise, can create any number of brahmanas, provided the candidates are available. The Gita-nagari, however, will not encourage the system of renounced order of life (Sannyasa), as in this age it is not possible to maintain such order of life under difficult circumstances.
-- Conception of Gita-nagari Part 2
It is worth noting that in the so-called "Gita-nagari Prophecy" cited above, Srila Prabhupada advocated the creation of a varnasrama society -- minus the sannyasa asrama. In an essay written several years later, Srila Prabhupada elaborated at length on the shortcomings of modern sannyasis. Who does not see reminders of ISKCON's own problematic sannyasis reflected in Srila Prabhupada's statements --
>> ...When Sri Ramananda Raya proposed about the efficacy of sannyasa either in the order of the Mayavadis or in the order of the Vaisnavas, the same was again rejected by the Lord for He thought that in this age sannyasa is an impossible game. The so-called sannyasis dress themselves in the red garments to earn an easy livelihood but in action they are like ordinary men of filthy mind. Such filthy sannyasis of the age of Kali may be able to accumulate large sums of money by the plea of establishing temples and deities by exploiting foolish persons but they are unable to bring their followers to Godhead.
>> ...These sannyasis generally construct some temples and install deities in them to exploit the religious feelings of different men but the main purpose of constructing such temples is to open different branches of income for comfortable material life although in the dress of a renouncer. They construct such temple most unauthorizedly and thus implore many foolish men to join to make contribution upon it. And some of them perform unauthorized yajnas and thus accumulate money. The temple builder sannyasi assures every one of the contributors to become the chief donor in such pious act but ultimately none of them is given any position but the sannyasi himself becomes all in all by accumulating a big bank balance for his personal material comfort.
>> ...At the present moment the whole procedure is miscarried and the preaching sannyasis themselves enjoy in the highest standard of material comfort while preaching the nullity of the same.
>> ...Sri Caitanya Mahaprabhu wants us only not to become one of the mudhas and Naradhamas. There are as many mudhas and naradhamas in the midst of the sannyasis as there are in the midst of so-called householders. Similarly according to the opinion of the Lord, there are as many mahatmas in the midst of the householders as there are in the midst of the renounced order of life. He is not very eager to turn anybody into the life of sannyasi from the life of a householder neither He is anxious to pick up spiritualists from the community of a particular class, society, nation, or group of people.
Ref. VedaBase - Perfection at Home -- A Novel Contribution to the Fallen Humanity
Later Srila Prabhupada went beyond the view that sannyasa is simply an "impossible game" in Kali Yuga. He declared that in general, people should be forbidden to accept the rigid order of sannyasa in this age:
>> ...In the present feature, the Lord is an ideal renouncer. He accepted sannyas and the principles followed by Him in that renounced order of life, are exceedingly wonderful. Nobody can be compared with Him as a sannyasi. Although in this age of Kali such acceptance of the order of Sannyas life is generally forbidden yet He accepted it because He was complete in this sense only. Others cannot imitate Him and therefore they are forbidden to accept such rigid order of life.
>>> Ref. VedaBase - Caitanya-caritamrta, Adi-lila, Chapter 2 [Handwritten]