I don't see Scale of Fates being better than any other run-of-the-mill spellpower trinkets. Assuming you're haste capped on your hots, what do you expect to be doing with that haste, spamming nourishes instead of hotting, or trying to get 1 second regrowths? Most of these abilities happen quicker than 2 minutes anyway, so the functionality of the trinket is unreliable.

You'd get more out of Eye of the Broodmother for sure, though I hope nobody here is taking that over a crit-based caster class like shadowpriest or arcane mage.

Sarth 25 is really easy to 10 man for an IDS. Use hibernate on the trash and its even solo-healable :P

How many healers are you currently bringing to your raids? Are you casting for every gcd or are there periods where you can get outside of five without ooc procs? Those two right there could well answer why you don't have any mana problems.

Either way there are a couple good trinkets for both throughput and regen from the hard modes. [Sif's Remembrance] from Thorim 10 hard and Show of Faith from Yogg 25 hard. The Show is 140 sp and 193mp5 for 15s on proc. Couple those with another regen trinket like the [Spark of Hope] and it makes the hard modes less stressful on your mana bar.

I'd be interested to hear how pressured you fell once your guild starts attempting hard modes in Ulduar.

It's interesting to note that [Pandora's Plea] is essentially the same as Show of Faith, only in reverse. The passive SP from plea works out to 141(vs 140 from Show). And assuming a 25% uptime on the show mp5 proc(15s duration assuming 60s cooldown and constant uptime, which would be generous), it is worth 48.25mp5... vs. the 108 intellect from plea which is worth 59.08mp5 ((108x.0175)+(108x0.162)+(108x0.210)).

Short version: 141sp 59.08mp5([Pandora's Plea]) vs. 140sp 48.25sp(Show of Faith), with reverse procs. Not considering the crit from plea because it is pretty much negligible.

With [Spark of Hope] pretty much demanding the first trinket slot, it basically comes down to those two for BiS second. And while Plea is slightly ahead number wise, some of you may choose to go with show just because the nature of their procs and how refreshing hots with additional SP works.

Personally I will be choosing Plea, as I feel the SP proc increases its value in the hands of a smart player who pays attention to the uptime. I don't feel anything else should even be in the conversation, unless you're talking about attainability. Then lesser versions/old trinkets can come into play.

I think a certain trinket that's attainable since day 1 of the xpac would beg to differ.

The new innervate is worth something along the lines of 215mp5. No trinket aside from spark is close to providing that amount of regen, so you can't overcome that deficit by trinketing for regen (my view might change if I do get a spark, but I haven't seen one so far).
I view innervate as an integral part of resto's mana regen, and I don't think your own innervate should be used on someone else. Other classes are should be built to be self and raid buffed sufficient; resto mana regen should be based about us innervating ourselves.
Even if I use the averaged out values that you computed, the tradeoff is 1SP for 1mp5, which isn't completely out of propotion (anyone who uses the 25SP meta is doing a worse tradeoff, for instance). Int is also a superior stat to 3 out of the 4 other healing specs, holy priests lagging behind with the druids.
Finally my original comments on IDS where posted pre-Ulduar. Clearly it's not twice as good as anything else now, but it's still a top contender for a trinket slot.

I agree with you that Plea may be hard for a resto druid to get their hands on as the intellect can be better for others then it is for us. Thats where the attainability factor would come in I suppose.

And I guess maybe I misunderstood your comment. IDS is certainly still top5, but they're are only two(one, spark is a must for BiS, no ways around it) trinket slots so I dont really see how that fits in to the BiS conversation. Guess it depends on what you mean by a contender.

For us Plea is a trinket you would use on General (hard mode) and almost nowhere else due to design of it - if you really want an Intellect trinket you might even be better off with DMC:Greatness(Int).

IDS remains the best throughput trinket for us while Eye of the Broodmother is a very good alternate version for other classes which get benefits from crit too (casters/other healers) and then there is Spark for the best mana trinket.
If for some reason you need to err more to throughput or mana on your trinkets then you have the option of switching one of them out for Sif's Remembrance or Show of Faith which are both good balanced trinkets to have compliment your primary ones.

Obviously, we trade off throughput for efficiency. Spark of Hope is such insane mana returns for druids (we use spirit and have 1 sec GCDs for a lot of our spells) that it is probably the most efficient way to make this trade (even more so than the meta gem). In other words if you have mana issues at ALL, you want to put on Spark of Hope first. I think IDS and Spark are our BiS for trinkets.

For what it's worth, I intend on replacing (or at least bagging) my Spark of Hope for Sif's Remembrance whenever I get back to doing 10 man runs. Spark is great mana regen, when we need it. But Show of Faith is great passive SP along with nice passive mp5. Mana hasn't become an issue - yet.

As our gear gets better though, our trinkets can be used to help pump out more healing, and as guilds move into hard modes and drop healers, we're going to need a ton more throughput. As things get moved to farm status, we'll figure out where we can conserve mana and how we can best live with Replenishment, Mana Tide, Innervate, and a Mana Pot.

For progression, Spark of Hope/Show of Faith might be the way to go - but as hard modes become increasingly easier, Show of Faith/IDS are likely our best two options.

Any thoughts on Spark versus DMC:Greatness(spirit)? Is there much difference between the two?

I currently have both as well as IDS. I've been equipping IDS+Spark. IDS stays for sure until I run into mana issues.

IDS will always be around so long as Vezax is one of the feature encounters. You should be able to stick with it for the pure SP(if so inclined) until you start hitting some of the latter hardmodes.