I would have to say it depends on the encounter. If there is a lot of raid damage (including you) and/or movement, I would say [Cowl of Winged Fear] is better because you have more stamina as a cushion and you won't miss the lower Spi since you will be moving around allowing for more OO5SR regen.
If it is simply standing still and healing pretty much non-stop, I would say [Helm of Anomalus] is better.
The principles behind these choices can be used with future gear as well. In fact, this is the basis most people use when they fashion mana intensive gear sets vs raw healing power sets. As you progress even further, you may decide to enchant the gear differently with Spi or MP5 enchants instead of Spell Power on a few pieces.
In 5 mans and heroics, it is fairly difficult to find a decent healing set that is full leather. As long as you are not taking cloth from a cloth-only class, I would assume that since a lot of the cloth pieces have the itemization that Resto druids need, you will be fine. Just remember that the mage, warlock, or priest in your group may get frustrated if you roll on a lower armor proficiency.
When you move into 10-25 man raids, it is best to just get leather. At this content, leather gear that druids need is abundant, and you will have no problem getting a set.
Since I'm casting instant cast spells a majority of the time, it ends up being up fairly often, increasing mp5 by a lot, although I don't have exact numbers. There have been times when this has been insanely useful.
Sorry if I'm a little bit off here, but I'm new to druid. I noticed as I was looking through heroic drops on WoWhead that a lot of times there were two items that were almost identical, the main difference being that one would have spirit and one would have crit rating. I've healed several heroics so far and never had mana issues. However, I know that 5 man encounters don't last as long as raid encounters. With that in mind, I ask you this; I have the talent that puts a healing seed on your target when you crit heal them, so I've been focusing on more crit rating. Would it be a good idea to get rid of that talent for a reduced mana cost talent or something and focus more on spi than crit?
Living Seed will largely be proccing off spells which you are talented for crit bonuses on and thus the effective crit rate on them comes primarily from those talents. This weakens the benefit of crit vs spirit even if all the spirit gives you is spellpower in tree form.
Heroic regen is, as you state, largely a non-issue and even in Naxx it largely isn't one. If you intend to jump into Ulduar or raid 10mans without replenishment you will want to have some extra spirit gear around to help keep your regen high enough.