For PvE, its potentially a huge boost.

For PvP, you will almost never want to always go Spell A, Spell B, Spell C, Spell D, and recast in that priority order as they expire. Well, maybe for Alterac Valley when you're dps is on Drek/Vandar, but that's about it.

Generally you'd want an FTL system.

Have Flame Shock on say button 1, for every toon.
Have Lightning Bolt, Chain Lightning, Frost Shock, Lava Burst, Purge, Lesser Healing Wave, Fire Nova, Grounding etc each on their own key too.
Have Thunderstorm and Earthbind on round robins.

Don't really go with click sequences or castsequences.
Just FTL spells, with one spell per hotkey, possibly a Wind Shock in there too.