Are there any decent specs that will allow me to fill both roles, without massively gimping either?
For background, my guild is very small, so we don't do raids. At the moment, I'm mostly doing random ICC 5 man runs for gear and emblems of triumph. That's the sort of level I'm working at, and I will probably move on to heroics once I've upgraded the last few bits of my gear.
Long answer: I seem to be one of the few who do, but as much as people keep trying to make them they are always missing out on something huge for one of the roles. also you have 5/5 furor, that is a big waste. Drop them in primal precision. drop imp mangle for either KOTJ or Pred Instincts (not a cat guy dont know which is better) and you still miss out on the other as well as 4% crit in cat and 4% damage in bear.
There's nothing wrong with going feral(tank)/feral(cat) with your specs unless your guild demands you keep whatever your other dual spec is. A full-breed tank and cat spec will always do better than a half-furry-butt spec -- not only is your talent pool used slightly differently, but your gear should be different. Right now, I'm carrying three sets of gear around -- thank goodness I'm a tailor and have all 22 slot bags. :}
That being said? I run a bearcat spec, because my guild _needs_ me to tree it up most of the time, but I occasionally fill the tank spot and the cat spot too depending on the fight and our raider loadout for the evening. I've gotten lots of help on fixing it in another thread here, but your best bet is to pick what you love the most and stick with it.
If you want to ultimately min-max, then yes, have a bear spec and a separate cat spec. For 99% of other situations, a hybrid is just fine. From a talent perspective, your biggest difference is in Master Shapeshifter, which I always hated given the waste of 3 talent points in Natural Shapeshifter. The way I see it, 5 talent points for 4% crit in a cat is pretty poor budgeting, as is 4% damage as a bear. Still, if you absolutely must min-max, it's there. I personally prefer having the flexibility to tank/dps/heal on the one toon, something no other toon can do without respeccing (not even paladins)
I once made a similar post here at Tankspot, and was pooh-poohed just as you were. Yet I have yet to find any problems with a hybrid spec. If blizzard didn't want you to make one, they would have 4 talent trees for druids. I think what really bothered me is that most of the people didn't even try to explain it, most people dismissed it without trying it. I have discovered the answers through my own experiences since that post.
You should be aiming for a spec something like this. You have a few points to play with, as follows:
-The Infected Wounds is a must for bears, unless you can have somebody else provide the same debuff (aka frost DK dps is the most likely candidate, possibly a warrior). If you do find somebody who can slow attacks, it allows you to pick up predatory instincts. Do not dimiss Infected Wounds, if you don't have that debuff, expect failures given that we eat a lot of damage as bears.
-Imp LotP is another situational one, you could drop it and put it into Predatory instincts.
-A common thing I see is people taking ImpMangle, which is normally a mistake. Likely these people take it to increase cat dps, which is wrong, you should be shredding instead. ImpMangle is good for bear threat, if you can spare the talent points. When making a hybrid spec, Shredding attacks first, then ImpMangle if you can spare it. If you do manage to squeeze in ImpMangle, DO NOT mangle your Combo points, use shred instead.
-Likewise Omen of Clarity is a cat talent. For one talent point, it shines.
You don't have the infected wounds or feral aggression abilities, which hurts somewhat as a bear; make sure to have a ret/prot pally around as well as someone putting up that slow. For cat, you're mostly missing NS/MS and the 4% crit ,which hurts. But otherwise it's pretty well effective for either and shouldn't be an impediment for bear or cat.
Hybrid spec's means you just suck at both roles. Out of all the tank classes we can pull this off the best... but that's still not saying a whole lot.
If you do decide to go with this, using a spec like the one Felhoof suggested is a good way to good, but I think one of the biggies that no one mentioned is gylphs. Probably the biggest difference you would see between each role would be what glyphs you got equipped. Getting a scribe friend to make a few stacks of Growl, SI, Frenzied Regen, Maul, Savage Roar, Rip, Shred and Mangle would probably go a long ways. The best part of this is that you can mix and match to the fight and your raid set up. (Which sounds like its in flux)
I used the spec felhoof posted (except moving the 3 points in Predatory Instincts into Infected Wounds) for awhile before dual spec came into play. I tanked and DPSed all the T7 raids with that spec, it works fine for both roles if you aren't doing endgame raid content. You won't set hearts aflutter with your performance but you won't "suck" either. If you don't want to swap out glyphs I'd go for Frenzied Regeneration and Savage Roar for your first two, best bang for your buck. Your 3rd will depend on the role you plan on playing most and the level of content; I'm a fan of Maul for 5-mans.
And if you find you don't use your Resto spec much at all, go ahead and dual spec feral. While you can do both roles adequately with a single spec optimizing for both will make a noticeable difference; your cat form in particular will thank you.