Nostalrius Begins - Quality wow vanilla realm (1.12)

Although I loved vanilla one thing I hated is how little the character screen gave about what each stat did and how much of diffrent stats such as +spell damage, spell crit chance you had.

Is there an add on that expands on your character stats?

There is one called combatstats and casterstats+bonusscanner and theorycraft. All of it in that "big pack". Not exactly like in future expansions but it does provide some info.

For healers you can use HealPoints:
http://armory.digam.dk/?sa=download.file.info&p1=3&p2=53

This displays your healing stats, including +Healing, and attempts to compare gear with what you are wearing to estimate if this is an upgrade.