I never thought the LAs were at all a core part of SavS; my assumption was that the monster classes, design-your-own-class, estimate-your-own-LA, and templates, feats, and spells were the main sell(s). The prefab LAs seem almost an afterthought, IMHO.
BTW: Half-fiend most certainly is worth ECL +4... once you hit ECL 8 or thereabouts. IMHO, no one should play a 0-HD creature with a level adjustment until one's class levels equal one's LA. At that level, half-fiend is worth it. Wings, resistances, SLAs, ability boosts, smite good... I'd say so. If you'd like a lower ECL, trim the wings and use it at +3.