considering your title... is your actual goal a high dex bonus, or is it a high bonus to hide & movesilently for sneaking around?
If it's the latter then you'll want to look at some things more than just racial bonuses... for example, the armor properties of
Greater Shadow (+15 Hide) &
Greater Silent Moves (+15 Move Silently) for only ~34k each
There's a nice little spell (if you can find some way to get it applied to you) called
Know the Shadows that grants a +20 bonus to hide when near shadowy areas, along with some other benefits.
Then there's a multitude of magic items that provide small bonus to hide &/or move silent:
Mantle of the Predator: +5 Hide & Move Silent
Rogue's Vest: +2 Hide & Move Silent
Bracers of the Hunter: +5 Hide
...
just to name a few...
And my favorites for maximizing your ability to sneak:
Ring of the Darkhidden - invisible to darkvision
Darkstalker - undetectable to scent, tremorsense, blidesight, etc without rolling spot/listen against the higher DC
I've got a Spellthief/Illusionist in a current camapaign that has a hide check of 77 (97 in shadows) & movesilent of 74... using the bonuses listed above...
also for a +1LA you really won't get much better than +4 dex... that's all I've got on my character from racials (with a +1LA) and she's near impossible to find once she rolls hide...