One of the easiest specializations to understand is that of the Sniper. The role Snipers play is very different from that of a Soldier, that much should be clear, and if you have the right characteristics as an individual and a soldier, you may be right for Sniper school.
As for additional pay, I know the CF lists pay grades including "specialist" categories, but wouldn't be able to confirm that a specialist is someone like a Sniper or not, though I would imagine so.