Interesting so the Assyrian "Orthodox" are definitely out. But the Oriental "Orthodox" are in? Both have been condemned by an Ecumenical Council as being graceless heretics. I wouldn't attend a non Orthodox Church if I was in an area that had absolutely no Orthodox parish. Why would I? I might as well go have bacon and eggs, or go bowling, or do any of a number of things.
Bottom line is, if you're an Orthodox Christian and you find yourself in an area with no Orthodox parish you should do services on your own, Matins, Hours, Akathists, etc.
Yes, the Assyrians are out, and the OOs are in. Yes, both have been declared heretics in the past. However, there is a difference between them. The EO and OO have always maintained a relationship, and always accepted that there is something grace-filled among the other. You can read the history about EOs and OOs accepting each other's clergy by vesting and their laity by confession of faith. Never, to my knowledge, has either communion had the regular policy of chrismating/baptizing converts from each other.
And now, in the last few years, much dialogue has occurred between the OO and the EO, and we have signed declarations stating each other's Orthodoxy and lifted anathemas. We recognize a unity of faith and are working towards the very attainable goal of full, eucharistic reunification. There has been no dialogue with the Nestorians, who have walled themselves off from the Church and are dying off. They have been cut off from the church, the OO have not.
Since I saw that you are ROCOR, let me mention that the Russian Orthodox Church, has been a leader in dialogue both with the OOC and the RCC. To my knowledge, the Russian Orthodox Church maintains the belief that the OO hold valid sacraments, as do the RCs. I know many ROC, laity and clergy, that will cross themselves when they pass a Roman Catholic temple in veneration of their Eucharist.
The reception by vesting has become practice due to the Unia and shifting borders. One year a parish could find itself under the Unia, and the next under the Moscow Patriarchate, therefore the priest was simply vested and received back into the Orthodox Church. I'm not sure that many OOs clergy would come into Orthodoxy through the Russian Church since it simply is not in their area, however the Greek Patriarchates receive Roman Catholic and Oriental Clergy by chrismation, and ordination through the ranks.
As for those decelerations you speak about, they are decelerations of meetings and conferences, not Church councils. Such statements are null and void, and they do not hold the authority which a Church Council holds. The council must be Pan Orthodox, all the representatives of the Patriarchates and Autocephalus Churches must sign and agree to the subject matter at hand, for example, that the Oriental's are really Orthodox. However even if that was to happen, it would be contradicting the decision of the 4th Ecumenical Council Which most Orthodox Christians on this forum I am sorry to say, blatantly blaspheme and ignore
and therefore, would also be null and void.
As for you what you said that the Russian Orthodox Church accepts Roman Catholic mysteries, in my experience with clergy both inside Russia and here abroad the consensus is that there is no grace outside of Orthodoxy. Metropolitan Hilarion of Volokolamsk it is true did say there was grace in the Roman Catholic Church, but this is his own private opinion, and it by no means represents the plethora of Russian clergy and laity who are very anti Roman Catholic. A simple glossing over of a Russian history text book
will show you how just anti Latin we are. Also, please note that the Russian Orthodox Church has said that the dialogue with Rome is going no where, and from henceforth we should simply strive to cooperate on moral issues and to fight secularism, not to talk about doctrine, not to talk about union as they are impossible goals.