Well, nothing wrong with your spec - it's exactly the same as I was using before I started playing with a 51/20/0 Divine Guardian.
As for HoL, well, every class/spec has some situations they just don't like and aren't suited for - doesn't mean they can't succeed, just that it's going to be hard. AoE damage is #1 on our list, and heroic Loken is the king in that regard. I've never actually done that fight as a healer, so no specifics, but your group needs to realize what it can and can't do and adopt a strat that works with a healadin even if they prefer a strat that is suited to a priest or druid.
Your gear is pretty good for where you're at, all things considered, not at all like some of the disasters we've seen lately. As you've noticed, you've lucked into some mp5 at the expense of crit, so emphasizing crit as you upgrade would probably help - but don't worry too much about sidegrading into crit or regemming (especially away from int, you want to get to and keep at least 19k mana, preferably 20k).
Spend some badges on the libram - the one you have is basically obsolete, with seals not only not being consumed by judgement, but lasting 30 minutes now...
Get a cheap (maybe even an old-school BC) enchant on your blues and a decent enchant on the purples. Don't worry about socket bonuses unless they're really tasty or you can do double-duty with the ones you need to keep your metagem active - at this point, 8 int is worth more than 9 SP and a 6 haste socket bonus...
Some crit-tastic upgrades from heroics, rep, or AH:
Chest - Scaled Armor of Drakos from Heroic Oculus, if you're up to it. It's another instance that's damn tough for a healadin, so I skipped it.
Feet - Skywall Striders off Ionar in Heroic HoL or the equivalent Mojo-Frenzy Greaves off Moorabi in Heroic Gundrak. Or the brass ring - Poignant Sabatons are a BoE drop from Noth in Heroic Naxx and the best available until 25-man Malygos. They'll cost 2k or so, but you can pass on every boot drop for months.
Finger - Ring of Temerity from the quest in Heroic Oculus. Forget how tough the instance is, for the quest you only need the first boss, so it's taking candy. There are also boss drops from heroic VH and AN that are decent.
Hands - The T7 gloves drop in both OS and VoA, so if you can sneak into a PUG (the standards are lower than for Naxx)... Other than that, there's a mail drop from Herald Volazj in heroic Ahn'Kahet.
Neck - Titanium Spellshock or Lattice Choker of Light, depending on whether you have more cash or badges. Either will last through Naxx-10.
Shield - Every shield in normal and raid instances has crit, and none in heroics, it seems. But the badge shield will last a long time.
Shoulders - Ferocious Pauldrons of the Rhino from Gortok Palehoof in heroic UK.
Trinket - Sjonnir the Ironshaper in heroic HoS drops Forge Ember, but inevitably you'll get the other trinket he drops, Spark of Life. Have you done the quest ("Last Line of Defense" in Icecrown) that rewards Cannoneer's Fuselighter? I still use it over the Alchemsist's Stone, at least while Crazy Alchemist Potions are still bugged and don't give the Stone bonus. If you're really rich, Darkmoon Card:Greatness will fill a trinket slot forever and will provide some crit as a side effect of all that int.
Wrist - Flamebeard's Bracers from Anub'arak in heroic Azjol-Nerub are a few MP5 away from being the best available in all 10-man content, including all three raids.
Good luck, and keep at it. Knowing your class and your capabilities is more important than knowing the specifics of a particular fight - that's what will help you when and if you are on a progression track in raids.