I know you haven't done it yet, but comparing it to the "other" cha based winged monster, the succubi has the better chassis, with TELEPORT. Fluff wise, both can get around in humanoid lands easily, due to one being outright invisible and the other assuming whatever the hell it wants, but the succubi doesn't have a negative stat, has the better abilities and can leave any unfavorable encounter at a moment's notice barring some extra legwork (dimensional lock) put in place.
Its a caster though, that moonlights as a scout, and that's only in social situations..... where scrutiny is more readily available. Personally I see it as a +1. The 6 hit die make it a bit more sturdy than the typical cha based caster, but cha based casters aren't the best kind in 3.5, and general, a level 7 Sorc or even Bard (yes yes I know, Warlock) can replicate the most useful abilities and have far more options on top of that. Half its abilities are geared towards a situation that its natural ability scores state it should NOT be in, with NO real built in damage mitigation, outside flight, which makes it even more apparent that it shouldn't be in melee combat. It NEEDS accelerated casting to stay relevant with the party. And outside of being a Diplomancer's wet dream (heh) doesn't offer the player much that they couldn't have gotten, looted, or crafted by the point the succubi becomes playable. The paladin succubi trope is cute (heh heh) but would of been far better served by playing some other race that didn't have any LA or RHD.
So yeah, +1 LA.