The answer, of course, depends on your raiding team.
The DPS Check
If you take a look around (via WoW Heroes for instance) and the bulk of your raiding team shows that they can still grab upgrades from ToC 10 and ToC 25 and you are knocking your heads against ICC 25, then spending some time on gearing up in those instances, while regularly doing the weekly raid quest and daily RDH for Frost Emblems may be all you need to get over the DPS hump.
On the other hand, if all your team's upgrades are to be had in ICC, and you're having healing and DPS troubles, your answer may not be so simple. There may need to be some fine tuning of specs and rotations to get you past the Upper Spire bosses. Or the issue may be strategy execution more than it is the DPS per se.
Alas, complex execution can't be purchased from a vendor. It is 100% dependent upon the time and effort your team is willing to put in.
There may need to be some dry runs of tricky strategies to work out good positioning, and allow folks to practice what they should do when they get marked with a spore for instance. (Hint: standing still where you are is not the right response.)There definitely needs to be no watching or talking on the phone while practicing. And to get the most bang for your buck, everyone needs to run back and rebuff and get ready to go for the next attempt quickly. This means no random AFKs, and being aware of what you need to do (buff the team, eat your food, renew a flask) before hitting YES on your ready check button.
Raiders need to keep your Vent channel clear and pay attention to the strategy and their role in it. If your raid leader asks you to do (or not do) something, you must be willing to act on it, not second guess it or worse yet, flat out do whatever you want instead without telling them. Basically, we're talking about trust here. The raid team needs to trust in their leaders and made a great team effort every time. This doesn't mean not speaking up if you have an idea for how to improve, but it does mean executing a strategy before deciding it doesn't work.
Working it Out
Trying to treat the illness before diagnosing the patient can only lead to frayed nerves and team tensions. It is on everyone on the team to understand their role, what's happening in the attempts, and if they die early, why.
- What's My Role? If you don't quite understand what it is you are being asked to do, it is always a good thing to ask clarifying questions. This is definitely a case of there are no dumb questions.
- What Strategy are We Using? Your group is going to be on the left -- does that mean the left as you run in or the left of the boss after he is spun around? Where are the healers standing exactly? Having a strategy that's spelled out (in words/pictures on your forums and read before the raid is preferable) can help decrease strategy execution mixups.
- Why'd I die? Sometimes it's a whoops! (uh-oh DPSer taunted a tank and died) -- own that and your team mates will respect you for it. Other times it takes some discussion to figure things out (Oh, the tank's healer got a spore and we didn't notice and pick up the slack on healing the tank -- whoops!)