Firstly, we don't mind answering your questions, except you kind of kept asking the same one which was answered a few times 
I started out with a Kraken as I said because, like you, I wasn't sure if I would get into it. I very much got into it and love riding but whilst the Kraken was a great bike for the money, I wanted something built better, lighter and stronger because as we've established entry level bikes = low end components, they don't last and are heavy.
Moving on, and I've mentioned it above, better components often mean, lighter, stronger and better quality so they work better. That's the advantage and that's really all there is to it.
Example:
The more expesive you get, the more of the below you will find.
Brakes - Better stopping power, modulation, lighter, stonger etc
Forks - Stronger, lighter, personal setup (sag etc) travel/damping adjust
Mechs Front/Rear - Lighter, Stronger, Smoother shifting, better adjustment option
It is the same for pretty much every part of a bike. To answer your question as to what advantages there are over certain specs, well that depends on the riding you're doing. Something good for Downhill or freeride might not be good for Cross Country (XC) or Trials.
Good sites? BikeRadar will be good to start with.

I started out with a Kraken as I said because, like you, I wasn't sure if I would get into it. I very much got into it and love riding but whilst the Kraken was a great bike for the money, I wanted something built better, lighter and stronger because as we've established entry level bikes = low end components, they don't last and are heavy.
Moving on, and I've mentioned it above, better components often mean, lighter, stronger and better quality so they work better. That's the advantage and that's really all there is to it.
Example:
The more expesive you get, the more of the below you will find.
Brakes - Better stopping power, modulation, lighter, stonger etc
Forks - Stronger, lighter, personal setup (sag etc) travel/damping adjust
Mechs Front/Rear - Lighter, Stronger, Smoother shifting, better adjustment option
It is the same for pretty much every part of a bike. To answer your question as to what advantages there are over certain specs, well that depends on the riding you're doing. Something good for Downhill or freeride might not be good for Cross Country (XC) or Trials.
Good sites? BikeRadar will be good to start with.