It's not the number of mechanics that is important (so long as everyone has sufficient flexibility). What is most important is what is the overall mana per time regen that the various healers have, taking into account all of their various mana regen systems (and including factors such as paladins casting several mana-free spells).
If you think one healer is struggling for mana compared to another, let us know. One mechanic we are still adjusting a lot is Rapture, because we want to make sure that the worst-case mana regen scenario for Disc still isn't all that bad.
I feel like mana regen in Cataclysm was very imbalanced for the duration of the expansion. Namely, Intellect based regen was OP in t11 and it only got worse as our gear got better.
Holy Paladins have been the biggest culprits. Holy Power providing mana-free healing, massive single target efficiency through things like beacon, and balanced the first two tiers around wearing little spirit means they saw constant increasing adjustments to their mana costs and still came out ahead of the other healers in the mana department. And of course, 4.3 Holy Radiance is egregiously overpowered, as any DS WOL ranking can attest to.
Druids are big offenders too. My Druid feels like he can spam Rejuv all day long and not care if he's hitting 40-50% overheal on that spell. Revitalize takes no brain power at all to keep up, and OOC procs a *lot* more than, say, surge of light, again, without any extra work from the Druid. They definintely get a lot from Inellect on live.
Shaman have suffered from low performance the entire expansion in PVE, and a lot of that is again due to mana mechanics. They don't have a mana cooldown (like say, Shadowfiend or Innervate) to themselves. So when they drop Mana Tide Totem, it brings them up to the other healer's baseline, while everyone else also benefits from MTT, putting them ahead of the Shaman. It is small wonder that Telluric Currents (supposedly "optional") feels like a requirement at the moment.
Disc Priests have benefited from a Rapture model that really loads on the mana, thanks to Intellect scaling. Penance is also highly efficient, as is PW:S if you don't go crazy with it. Again, small wonder they poo-poo on Spirit gear.
Holy Priests have been the "Spirit Healer" for most of the expansion. It wasn't uncommon to see Holy Priests stack twice as much spirit as the other healers, and still feel like their mana was behind (especially in 10s). I feel like a lot of the efficiency of Holy is tied into Lightwell and Divine Hymn, so if those two spells aren't able to do the heavy lifting for Holy - like say, spread fights or heavy movement - Holy suffers. Holy spends a lot more item budget on Spirit than the other healers - which would be fine, if we were compensated for that by having stronger heals than the other healers. But that isn't really the case, which is why Holy has been behind since the POH nerf back in early Cata.
Chakra also contributes to this problem (especially in 10s) because we are locked out of the most efficient versions of our spells for 30 seconds at a time, and situations that call for switching between, say, Greater Heal followed immediately by Prayer of Healing simply happen too often (again, especially in 10s). Holy, ironically, has the most spells, but the fewest useful tools in a real-world situation. In 25s, it is less of a problem because the answer to "what is the best spell" is always POH.
In the MoP beta it sounds like healers are keeping their "extra" mana regen mechanics, except for Priests;