Its really hard to say, if you gear up your shamans too much your pally is going to have a hard time holding aggro, you can gear up your pally first of course but the shamans may not have enough damage to kill stuff fast enough.

Maybe you should decide what your goal is first? I'm leveling 4 shamans (62 atm) and my goal is to prep them for wotlk so I can level pally+4 shamans to 80 first. Anything that helps that goal is primary, anything that doesn't isn't important.

So for example I do plan on getting the s2 gear because it'll stay useful till at least level 65, and be good for instance running. I am not going to focus too much on arena, s2 is good enough and I'm not that great an arena player. I will run some heroics and instances, maybe the daily if its easy, but not spend too much time on this - the badge gear is nice, but I don't need top of the line gear on all my characters. I am not going to worry about Karazhan and 25 man raiding at all.

Now one thing is that my pally is very well geared, he has both a great set of holy gear (+1800) and prot (~14k hp). Hes been my character since TBC though and he was holy only for a long, long time. Its much easier getting into "badge" runs (2 hour kara, 1-shot gruul/mag) pugs as a mediocore geared healer than a tank. A few weeks of making sure you clear kara/mag/gruul every week and you'll have a new badge gear epic, plus you can run the heroic daily as a healer for a few more. With your tank gear, I think you'll have a much harder time getting into groups as a tank, at least groups that don't wipe a lot. Of course getting a bunch of healing gear isn't trivial either

If you are good at farming gold with your alts you can get a bunch of good pally tank gear, like the epic BoE belt, the furies deck, the BS or engineer helm, and probably more I'm forgetting. imo getting the pally geared up is the cornerstore of doing heroics and 5 mans, but thats not as important for getting geared up for WOTLK (although having a geared prot pally would help a lot imo)