There are two of each spell but in reality there aren't many spells. And with the augmentations to AoE coming, you can safely split AoE and Single target bars if you don't want them all on at once:
But really, RDM still fits on three bars if you don't use separate AoE and ST bars, and there's even room for Magick Barrier (place held here by Shield Samba):
In practice there is very little RNG to RDM and even when you can't force a proc with Acceleration or the correct Verfinisher, the nature of Dualcast gives you plenty of time (t>1.8s) to decide which spell to use next.
The extra 1 mana from using a VerAoE spell is not worth the lost damage from ignoring Scatter. In AoE, 1 mana is only worth 1/40 of an Enchanted Moulinet, which only does 134p over what you would do with an average AoE spell in the same amount of time, so you'd be giving up 20p of Scatter damage for 3.35p of E.Moulinet damage. It's not a good trade. It's even worse when Scatter becomes Impact and the difference between Impact and a VerAoE spell jumps to 100p.