Tourism contributes about 30bn a year to Turkey's economy. That's about 30 million tourists. Turkey has a PPP GDP of over a trillion. Tourism isn't all that important. Iran has lots of energy, and a starved (from investment) population of 80 million. Meaning there is plenty of growth in aviation, regardless of tourism.
Beach Tourism is basically the worst kind of tourism, most of these tourists are people who cant afford expensive holidays so they go to all inclusive hotels including flight ticket, they eat, drink and party in the hotel and barely go shoping.
Thankfully we have also a good amount of City tourism in Istanbul which is clearly more profitable, since Turkish series went popular in ME Arab trousists are overrunning Istanbul and they spend at least 4-5 times more in Shopping centers than Europeans in Antalya.
Also there is a good amount of backpacker tourists in Cappadocia with a good amount from Asian countries such as Japan and Korea.
You can split the tourist groups in Turkey such as:
Beach Tourists = Europeans, Russians, Baltic states
City tourists = Europeans, Japanese, Chinese, Koreans, Americans
Backpackers = Japanese, Koreans, Europeans
So there is two options for Iran to increase tourism, either with all inclusive beach resorts which is a very bad sector or Cultural tourism.
Either way mass tourism such as in Turkey where basically tourist numbers as big as half of countries population need very serious infrastructural investments, Istanbul has two international airports (30M and 20M capacity) but its handling about 90 million passengers annually and they already stated to build a third one with 150 million capacity.
Now first try to imagine those numbers, even thought many of the passangers will take the next plane and fly somewhere else most will use a street or public transportation to arrive their destination so you need to invest in those too, thats investment in hundrets of billions just for the state, adding to that that you also need private investors for hotels and such stuff, it isnt a easy task and wont be cheap either.
So just buying 500 planes wont make tourist come you also need to offer them some sevice and infrastructure.
But before discussing all those, just as mentioned above, the domestic laws and rules would prevent most tourists to come to Iran in the first place.
Tourism isnt the most profitable sector for sure but its a huge inverstment in PR so i wont rule it out too quickly.