Correct, Dolphin is just it's own stand alone emulator right now. I believe there are plans to have a Retroarch core somewhere down the road but that is a ways away still.
The best way to get Mame looking better is using either GLSL or HLSL shaders.
Lol. I can't and won't even try to tell you what to do about Launchbox and Rocketlauncher but you can keep using both. Just for the record though I do not use Rocketlauncher because I do not care about the extras it brings such as bezels, load and pause screens.
I would say if you are comfortable with Rocketlauncher keep using it, you can still use Retroarch through it if you wanted anyways so you won't be losing out if you want to use RA.
What exactly are you using Xpadder for ? I have Xpadder installed but I use it very little if ever outside of Daphne or an oddball game that doesn't have controller support.