Depends oddly enough, on the state of Egypt. If Egypt is part of a Greater Arabia, or Ayyubid state, then the Levant is vulnerable.
If Egypt is independent, then apart from the question "Why not conquer Egypt" then the Levant is more secure.
I think the prospects by and large are good, but ideally the Romans need to be active in preventing any other polity becoming too powerful near the Levant.
(Which, in my mind, always leads to conquering Egypt and Mesopotamia, at least as client states).
The additional wealth the Levant provides will be useful, but not as useful as controlling access to the Red Sea. They have control over the Persian silk road which is great however - but the long borders of the Levant make it difficult to defend.
TL;DR Depends on the surroundings, the more fractured their opposition the better - so the best scenario IMO that meets your conditions, is a v.difficult war, that exhausts both the Romans, and a single great king in the Middle east, whose death leads to a massive period of civil unrest and independence movements, shattering the Romans opponents, whilst they are unable to take advantage of the circumstances.
Personally, I like the idea of the enemies of the Empire split between a strong Egypt, a strong Mesopotamia, a strong Iran, and strong Arabia. None can risk invading the other without someone else intervening, and many have economic reasons to co-operate.