I noticed that many prestige classes for caster classes allow an increase in one of the player's caster class levels, but doesn't provide the benefits/class features of taking a full level in that class. Consequently, does a Sorcerer, who has no class features to begin with (save the first-level Familiar or Metamagic Specialist), technically get a full level of Sorcerer from such classes?
Your Familiar only improves with Sorcerer levels, so a Sorcerer 10 has a stronger Familiar than a Sorcerer 5/Prestige Class 5 (unless, of course, the Prestige Class explicitly advances your Familiar, which a few do – Alienist from Complete Arcane and Fleshwarper from Lords of Madness, for examples).
But other than that, no. Sorcerers generally have nothing to lose and everything to gain from going into a full-casting Prestige Class.
Of course, be careful about prerequisites; a number of them can be quite painful to Sorcerers (who lack bonus feats and cannot trivially pick up the ability to cast a given spell the way a Wizard can). A classic example of this is the Loremaster: in theory, the class is 10 levels of free class features for the Sorcerer, but in reality you have to burn several feats, somehow get 8 ranks in cross-class skills, and find seven different Divination spells worth spending your extremely-few Spells Known on. (The Wizard, on the other hand, can get in while barely trying, thanks to his class skills, Bonus Feats and arbitrary number of Spells Known.)