I think they need a lot more help than that. Even the 2E thief is barely viable, and the existence of thief skills create problems as to what other classes can and cannot do.
Knock, elven boots and fly duplicate their abilities, and what they can get away with in combat with regard to their skills is subjective, and only hinted at by the rules. Thieves are, in short, problematic. If not completely overhauled or relegated purely to NPC henchman status, perhaps they're best ditched entirely.
Well, since you opened up that can of worms...
Yes, the thief class has never, ever, been executed properly. In theory, he's supposed to be an slick skillful adventurer whose role was a scout, explorer, and secondary fighter. He's never been that. Magic routinely trumped his primary roles, and his combat ability has never been worth a bucket of warm spit. In AD&D (1e and 2e) thieves made great X/Thief multi-class characters, where X is fighter, mage, or both, but single class thieves often began to lose their luster from 5th-9th level (right when magic becomes ascendant).
FWIW, fighters end up in the same boat around 12th level.
At least third edition rogues made attempts to balance rogues (class abilities like evasion, better skill rules, sneak attack) but in the end I rarely saw high-level rogues even in 3e. 4e's look interesting because, for the first time, they are expected to get into melee and deal damage.
I said back on page one I'd love to play RC D&D again. This is somewhat true; I would, but I don't think I could make a long-running game of it. Too many little fiddily rules (like how thieves work or demi-human level limits) would make me irritated to the point of wanting to move on to another iteration of D&D (3e, 4e or C&C) eventually.
Guess you can never go back.
