- Secure Mikawa
- Secure Narumi/Odaka line
- Capture Owari
To be fair here are some information to back the answer.
Hashiba Akira's Shinsetsu Okehazama Kassen lists three conflicts with Nobunaga during the 1550s, pp. 75-89.
- Battle of Muraki 1554
- The siege of Kanie Castle
- Assault of Ise
A survey done in 1598 showed Owari was a productive province. (Koku)
- Suruga 150,00
- Totomi 255, 160
- Mikawa 290,715
- Owari 571, 737
With new evidence pointing towards Owari, I still think Kyoto was the target. I think Yoshimoto was alarmed that Uesugi Kenshin went to the capital twice. In 1553, he met with Emperor Go-Nara and in 1559 met with shogun Ashikaga Yoshiteru. Nobunaga also met the shogun in 1559 as well.
Hamada Akio's Okehazama no Tatakai: Kagetora no Kakuryaku to Nobunaga no Sakuryaku is a who pulled the trigger book and I think there is some truth to this. The book also goes in depth of Yoshimoto's alliance with the Takeda and the Hojo. Kenshin and Nobunaga's trips to Kyoto and the three way alliance between the Imagawa, Takeda, and the Hojo might have pulled the trigger for Yoshimoto to march to Kyoto for once and for all.
Yoshimoto also spent time in Kyoto when he was training becoming a Zen priest with his partner, Sessai. Yoshimoto's mother, Jukeini, was a daughter of a court noble. Yoshimoto's aristocratic blood and lifestyle made Kyoto the perfect match. Yoshimoto had the chance of a lifetime and I think he trying to take full advantage of it. If any other Sengoku warlord had the same opportunity as Yoshimoto did, I bet they would taken the chance as well.
The downside of the Kyoto campaign would be the several families that Yoshimoto would have to deal with. Families such as the Azai, Asakura, Miyoshi, Rokkaku, and the Saito. Still, I think Kyoto was Yoshimoto's destiny. I may be wrong, but that is my opinion and sticking with it. Sure movies, novels, and the like portray the objective was Kyoto.
I based my opinion on what I know and feel. Again, I may be wrong, but I also respect the opinions of others who disagree with me. Kyoto was Yoshimoto's destiny, but his dream was evaporated at Okehazama.
Nobunaga no tame!