This is such an interesting topic to me, as it seems like the 'question behind the question' is something like "What is or isn't appropriate for Patriarchal Residences?", or maybe even "Why have Patriarchal Residences when they 'look bad' and that money could be used to feed the poor?"
I obviously can't answer these, as this is on TAW and not in the St. Justin's subforum, but reading this thread moved me to read the article on Patriarchal Residences in the Coptic Encyclopedia, which states that the Patriarchal Residence of the Coptic Pope has moved seven times since the time of our evangelist and master St. Mark (I thought it would've been way more often than that, what with all the turmoil in Egypt and the antiquity of the faith in the country), and the current residence at the new St. Mark's Cathedral in El Abbasiya in Cairo (consecrated 1968) is built upon the former site of Deir El Khandaq ("Monastery of the Moat", est. circa 970, called that because it had a moat around it dug on the orders of General Gawahar El Siqili, the founder of Cairo, for strategic military purposes in his fight against the Qarmatians, a rival Islamic sect to his own). Long before this there was a tradition (attested to in EO sources like the Chalcedonian Patriarch of Egypt Eutychius, 877-940) for centuries that Coptic Popes would reside at the monastery of St. Macarius the Egyptian (Deir Anba Maqar), est. 360. It's not known when this tradition started (which eventually required the Pope to be enthroned not only at Alexandria or Cairo, but also at the monastery of St. Macarius), but it didn't end until 965, when the seat was moved for a decade to a tiny village known as Mahallat Danyal (Site of Daniel), which doesn't exist anymore but was in the area of what is now the district of Kafr El Sheikh, about 85 miles north of Cairo, in the Nile delta.
My point in all this is not to spew Coptic stuff all over the EO board, but to show that it seems that Patriarchal residences of some kind have existed for as long as there have been Patriarchs (I'm assuming that of our holy father the apostle St. Mark was probably for a time the house of his successor and first convert St. Inanios, as the apostle had been welcomed in by and converted his family), have survived the major schisms, and have actually sometimes probably been as humble as the OP and apparently others think they should be. I can't imagine that living for a decade in some village essentially in the middle of nowhere outside of Cairo instead of actually in Cairo (which was a possibility by that time), or in Alexandria (where it was already established) or in Deir El Maqar (ditto), would've been all that luxurious or fun.
But there have always been Patriarchal residences. I suppose the only difference here is the price tag and the accompanying sense of unease, but as others have pointed out, it is part of the Russian government's restoration of the site as a historic building. Should your Patriarch not be allowed to host foreign visitors and dignitaries in such a building? Why not, if there is cooperation with the authorities in this? What law does it break, either by Church canon or secularly? Are there EO canons that say that what is being done here is not allowed? (Serious question; I'm asking because I don't know.)
It'd be one thing if HH Kirill had ordered it himself, like "I want this multi-million dollar mansion for myself, because I'm the Patriarch, so I deserve it, blahblahblah", but that's not what's going on. So even in a mansion, one may be humble. Humility comes from inner control of the passions guided by the Holy Spirit through submission before God, am I right? And I don't see how anyone could possibly see into HH's inner parts to know where he is in his own struggles and prayers. Certainly that's not knowable by looking a at a building. I feel confident saying even without being EO (purely because I know actual EO in real life, so I know the examples they set; not meaning to 'teach' here) that this is not what the EO faith is about. If HH had a different, more modest building in which to welcome guests and such, it'd be the same faith. If he converted it to low-income housing or whatever the "Churches have too much wealth" crowd want, it'd be the same faith, etc.
Am I wrong here? There's nothing wrong with Patriarchal residences, they are extremely historically sound (i.e., not an innovation -- for those who worry about innovation creeping into your Church), and if this is another one of them, then who can say it shouldn't be?