If you want something balanced, don't use SS.
Monster PCs have abilities that are not balanced when given to a PC. You can't balance the PC by making him weak in terms of hit dice and strong in terms of powerful abilites.
Take, for instance, the ghaele. If you play a savage species ghaele up from 1st level, it really unbalances a party. Why? because it has a bunch of abilities that PCs are not meant to possess.
First of all, it can fly really fast over great distances. They just made a huge effort to take high speed flight away from PCs in 3.5.
Then, look at the gaze attack. This really screws up combats. The enemies start fleeing the PCs instead of fighting. This makes combat into a hassle.
The DR is also a problem. When you give DR to a monster, the PCs often can muster up a way to bypass it. On the other hand, monsters and NPCs have less resources than the party. They will rarely be able to bypass the DR. This makes these abilities far more powerful in the hands of PCs. In very few situations will a ghaele's DR be different than a 34th level barbarian's DR. This makes them invulnerable to creatures with low damage, but multiple attacks and disproportionately vulnerable to creatures with fewer, yet stronger, attacks.
The flip side of this problem is the low hit points / hit dice of the ghaele PC. At medium or high level, the ghaele PC will start dying at a fast rate. Enemy spellcasters will hit it with PW: Kill, Blasphemy, etc ... Enemy fighters will take it down in one full round of combat. An enemy rogue might get it with one well placed sneak attack.
You can't balance a character by giving it great strengths and great weaknesses. You'll either need to accept that SS creatures will be out of balance in many ways at all times, or decide not to use them.