The problem with watching for OOC is that it doesn't appear until you finish casting the spell that triggers it. The only way to intentionally benefit from it is then to interrupt your current cast (which you should be timing with Quartz) to cast a higher mana cost spell. The gain in mana efficiency is directly offset by the loss of DPS from canceling your casts. The same goes with Eclipse; it's always higher DPS to continue your current cast rather than cancel it and switch to the other rotation. Now, if an instant like MF or IS triggers OOC, then you can switch up to take maximum advantage of it.
Eclipse lasts 15 seconds and has a 40 second internal cooldown. Without an addon to track it (which would be a good idea in and of itself), you have to mentally time the cooldown if your intention is to always use Wrath to proc the Starfire version. The alternatives are to simply alternate between chain-casting Wrath and Starfire as each Eclipse proc occurs, or to always cast Wrath unless the Starfire Eclipse proc is active. Either way is acceptable and depends on your preferred style.
Math: 15/40 sec = 37.5% uptime (optimal). The Wrath proc increases damage by a flat 20%, while the Starfire proc increases crit by 30% - assuming 40% already, that's a net 22% increase. Eclipse's value as a talent is therefore worth about 8% net DPS increase at perfect uptime. In practice it's going to be less than that.
FYI, the theorycrafting I read on Elitist Jerks says that with any amount of haste, the cast time on Wrath is still faster than the reduced GCD from Nature's Grace, since it can't go below 1 sec. Therefore, chain casting Wrath is a less efficient use of NG than chain-casting Starfire, which makes up for Wrath's higher base DPS. There's also the fact that Starfire with the glyph extends the duration of Moonfire, giving it additional value. (9 sec extension of a 15 sec base = 60% extra damage per Moonfire cast.)
I wouldn't be surprised if all this makes your head spin a bit. Balance Druids have one of the most complicated spell rotations in LK now, and you practically need a math degree to figure out the value of each talent.
I should also add that I was amazed by the amount of mana regeneration provided by Moonkin Form. It's actually by far our strongest talent point both in per-point and net benefit, and almost makes Dreamstate and Moonglow obsolete.