The World of Warcraft has a lot of things to do in it, but a majority of those things come down to items. For good reason, too. Things feel more rewarding when you have something physical to take away with you. As physical as virtual items can be, anyway. For example, I think Badges of Justice from 25-man bosses is fantastic. Even if you go weeks and weeks without seeing 'your' items drop, you'll be gathering badges. You may not even need the badge loot, but you can at least get gems, nethers or whatever ekse to put on the auction house. 'Physical' rewards are fantastic- they make you feel good.
The WoW team's philosophy on bag space works directly against this, limiting how many of those fun things you can have. For people who enjoy collecting vanity pets or pretty dresses, this limits fun. That is bad. This situation is much, much worse for the hybrid classes, to a greater or lesser extent depending on what you play. At some point, most every class probably needs more than one set of gear if you do more than solo. Even pure DPS classes need a bit of resist gear in the end-game, or perhaps you carry around pieces with more +Hit or more +Crit or whatever else. The Hybrids, you're looking at Tank gear, Healing gear, DPS gear, Resist gear, etc etc. Not every class needs all of those sets, but many of the hybrids do.
Assuming you never wear a shirt or a tabard, you have a potential 17 pieces of different gear for each of your sets. If you're a Feral Druid, you're going to want Bear gear and Cat gear, bare minimum. You most likely also have a Healing set. That's 51 pieces of gear you will usually have with you if you're grouping/raiding heavily. If you're really min-maxing, you may also have partial additional sets for more Stamina or Expertise when the situation demands it. Add another dozen or so pieces of armor onto that list. We're up to 63 pieces of gear.
Then you have reagents. If you're in a raid, you probably have about three stacks of Wild Quillvine and a couple stacks of Flintwood Seeds. Two types of elixirs, at least two stacks of mana potions, buff food, regular food, and water. That's five slots for the reagents and a minimum of seven slots for consumables.
We're up to 75 bag slots. Just for things you need to carry with you for content higher than 5-man dungeons. With the basic 16 slot bags that everyone should have in Outland, you have five free inventory slots. I hope you didn't want to be able to loot vendor trash or carry a pet with you!
When you need to carry that much gear with you, the size of the bank is almost irrelevant. As a roleplayer who likes being able to play dress up every now and then, I still don't think the bank is big enough, but as I said, it is almost irrelevant. You can't carry your bank with you wherever you go.
There are options out there for increasing your inventory space. In my very long-winded example above, you're using basic 16 slot bags. At 70, though, you should be using at least 18 slot bags and working on 20s. This can be a pretty expensive endeavor. 18 slot bags on my home server are generally 40 gold each. Not too bad. 20 slot bags, however, are around 500 gold. You could be spending 2,000g for a full set of 20 slot bags.
I have good news!
While even full 20 slots can be terribly limiting to a gear-intensive hybrid, it won't cost you a lot of money to get them anymore. Patches 2.3 and 2.4 have been kind to us on the bag scene. In patch 2.3, Zul'Aman was implemented, and with it came the Tattered Hexcloth Sack. I'll let you in on a secret: You, personally, do not have to do anything substantial in Zul'Aman to acquire this bag. You do, however, need to be friends with someone that has.
To get that bag, you simply need to pick up the quest outside of Zul'Aman, skippity hop into an instance cleared up to the quest item, and pick it up. Grats on your new 20 slot bag! Absolutely any brand new 70 can get this quest. Your 'scrub' alt in auction house greens can fly up to the Ghostlands and get this bag.
Patch 2.4 takes the bag love a little further. There are two new 20 slot bags in the patch, though they will take more work on your part. The new 5-man dungeons, the Magisters' Terrace, drops the Sun Touched Satchel fairly commonly off of the trash mobs in the instance. Pretty straightforward.
Additionally, the heavily nerfed Magtheridon will drop a 20 slot bag, the Pit Lord's Satchel. Why Magtheridon's jailers let him hang onto his purse, I'm not quite sure. Then again, Onyxia carried a bag created out of her own skin, so it isn't the strangest source of bag space in the world. This bag is not unique, meaning you may have more than one of them. You are going to be competing with 24 other people for the drop though, so don't cheer quite yet. It may take some time to get one!
Does this solve the bag space issues? Not quite, but it does help. Bag space remains pretty limiting, especially for hybrids. These new bags do lower the cost of convenience, and it does make things a bit less frustrating. Going by the prices on my server's auction house, getting one of each of those bags will save you about 1500g. That's no small amount of money. Okay, so maybe it is pretty small nowadays with daily quests, but at least it looks like a big number!
Though it may never come due to bagspace being a mini-game and the database issues additional space may cause, I dream of a day where my Paladin can carry around all of her necessary sets of gear and a pretty dress or two while still being able to loot vendor trash. Hey, even the manliest of men get the urge to dress like a princess sometimes, alright?