I FINALLY unlocked the dialog from the Jarl!!!
It had nothing to do with the list posted above. I had to complete the mission called "Locate the Assassin of Old" under the misc missions. After I completed this I returned to the Jarl, like I do after every mission, and he had the new dialog. After that I just had to get him some Black Briar Mead and it worked!!!! Finally!!
Lol I was having this same problem, I am Thane in just about every town, never had a problem until now. After taking your recomendation to buy Hearthfire, I built my first house, Winstad Manor, after becoming Thane of Morthal. It was not my first choice, I couldn't get the Dialogue from the Jarl in Falkreath to buy property so I went to Morthal instead.
After building all 3 wings on my Winstad house, I took a break to do more side quests. Then I focused on Falkreath again, and for the record, Bounty quests given DO NOT count towards being able to buy property.
What ended up working for me is going to the Halfmoon Mill and chopping wood there for the lady, Hert is her name (too bad you can't marry her, she is one of the best looking NPC in the game). I learned that you do not have to just help people in Falkreath, any place in the Hold's territory will work. After I chopped the wood I instantly went back to the Jarl, there was instantly a new dialogue option and he gave me a request for Black Briar Mead. After delivering the mead (from the Tavern in Falkreath, you do not need to go all the way to Riften), he game me another quest to Kill a Bandit leader in the Embershard Mine, after that was complete I was given the option to buy the Land from his assistant.
I am still not Thane of Falkreath, you do not need to be Thane in order to buy the property.
