Viability of a Spell Speed WHM set up?

[Tranquil]

Secondaries on a healer are literally meaningless.

They are not.

I'm sure you've heard before that skill trumps gear, and this is most evident on a healer.

Now, this I do agree with.

OP, you could go for SPSP for fun but it's not a good stat. If you intend to chain cast DPS-spells, go ahead. However, for your healing game SPSP has very little effect as healing in this game is very timing-based with little to no chain casting necessary. When you are not chain casting, you are not really getting anything out of SPSP. That marginally faster Cure II won't be helpful because, y'know, you could have timed it perfectly anyway via precasting with some thought. :')

There're tons of SPSP-related topics on this forum and the efficacy or lack thereof has been exhausted in previous topics, whilst some still advocate SPSP.

TL;DR: WHM is your offspec, have fun with it and do as you please.