What your referring to as Persia in this Era was the Parthian or Arsacid Empire (Seleucid Empire in the early years). Which came into existence around 270 BC and fell to the Sassanids around 225AD.

The Parthians were an interesting empire that at its height was the military equal of Rome. They were a group of independent kingdoms (City states) that were ruled by a local king, and the council of kings would then elect a king of Kings. The King of kings could technically muster all of the kings for a common cause, but in practice this didn't often happen, and resulted in various alliances and war within the kingdom itself.

Relations with Rome went from sour, to peaceful, to sour, and so forth as each kingdom consolidated power. A common misconception that people make is that Parthia was a weak nation, protected by its desert borders. The reality is that much of Parthia was extremely wealthy. Mostly because of trade routes between China and the Roman empire that all ran directly through Parthia, and taxation made them wealthy.

Parthia and Rome often came to odds over Armenia, which at first was a Parthian ally and later a Roman subject state. Mutual distrust started early between the two nations but neither could really hope to totally defeat the other.

Parthia also had a highly developed aristocracy, and as such looked down completely on anyone who was not Parthian, and had a very distinct class system. In short the Romans thought that they were superior and the Parthians believed in their own superiority. Several early engagements between Parthia and Rome only heightened this sense as Parthia devastated Roman Legions at Carrhae and earlier in more minor skirmishes outside of Dura Europos and Hatra.

In the late period of the Parthian Empire, there were a few kings who took roman gold to become "allies" of Rome, but this was almost a necessity since they had been weakened by years of civil war, and had no hope of stopping a roman invasion. Especially with the Eastern kingdoms being pressured by the Sassanians.

So in short, Parthia had as much of sense of self worth as Rome did. And while there are always exceptions to this rule, Parthian High Kings were generally very Anti-Rome. Some sought peace, others looked for war, but very few if any wanted subjugation. Parthia has always been intriguing since it tangled with some of Romes most famous faces (Pompey, Crassus, Antony)

This is a good read for the various changes of diplomacy between Parthia and Rome, and the conflicts that developed through the years.

http://www.allempires.com/article/index.php?q=war_roman_parthian#2

The wiki has some good info on parthian Society and

http://history-world.org/parthians.htm This has some great info for a general sense.