Do the post level 50 specalizations provide anything apart from armor?

Yes the specializations unlock unique bonus armor mods. They also get an armor, armor variant, weapon skin, and a set of visors.

The armor mods provide the following abilities.

• Engineers get to see weapon drops early
• Operators reduce the effects of plasma pistols on vehicles they drive, and reduce the chances of getting hijacked.
• Pathfinders reduce weapon heat-up on turrets and move faster when carrying them.
• Pioneers get experience bonuses.
• Rouges have increased weapon stability when under fire.
• Stalkers get the person who killed them last lit up on their HUD
• Trackers get better ordnance drop options.
• Wetwork allows for reduced stealth detection from motion sensors and Promethean vision, and they get faster assassination animations.

From the wiki.