I've been using the Egg and
Majestic Dragon Figurine.
With us Druids, since you figure to spend 3 lifeblooms starting out the tank, a rejuv and prolly a regrowth, then you fall into the refresh/top-off mode, it's pretty simple to get this trinket maxed and since we will always cast another spell while in combat before the 10 seconds is up, it just refreshes the stack.
180 Spirit pretty much constantly in combat is a nice boost. Plus you get the added benefit that spirit has to your heals, which ends up being 27 spellpower once it's at a full stack. It does drop off Sartharion, which may or not be in your range of raiding.(You said you don't raid much)
However, Sarth with no drakes up is a pretty simple fight to pug on most servers at this point, although still requiring a decent amount of coordination to ensure people don't get hit with fire walls.
As to why the Egg is better than the DtK trinket. The 73 Spirit is nice, if you are having problems with mana regen, but if not, the static 98 spellpower from the Egg, as well as the Haste buff, which is up rather frequently, ends up having a greater overall effect during boss fights than a 20 second on use trinket.
HOWEVER, since you don't raid as much and mostly do heroics, the DtK trinket may be better individually for you.
As far as what to use till you get an upgrade, I'd say Cannoneer's Morale as testing on Valonforth's Rememberance has shown that it hasn't been proc'ing on Instant cast Druid spells since 3.0.8. Would love to hear if you're getting it to proc off a lifebloom or a rejuv. IMO the Cannoneer's static Mp5 + on use SP boost is nicer anyway. Sometimes just having a bigger heal saves you from casting another heal which is like having regen without needing to regen :P