The $30 price tag gets you a $10 discount as opposed to buying the 4 individual DLC at $10 a piece. Simple as that.
You can buy now and save on the long run, or you can wait it out and buy the pass later...Or worse still, spend more money buying individually.
The 4 expansion packs are going to be more than just 20 minutes of cheesy DLC. Given BL1's history, they add a significant amount of content that is actually worthy of the price tag. Expanding a good deal on the original game, increasing level caps, adding new rare loot, and so on. Hell, more skill points to let me dig my nails deeper into these skill trees are worth it alone, IMO.
Plus you can go buy it for about $22.50 from GMG when they have one of their many 25% off coupons going. That's nearly half price of buying the expansions individually.
In total, I would think that as long as you think the base game is worth $60 or is good value, the DLC will *probably* end up being worth $30. 4 expansions should add quite a bit of extra playtime, the first one alone looks to have a few new raid bosses (or something of that scale)...
If you think the game is overpriced from the get-go then the DLC probably won't save it. But otherwise this should end up being worth it.
BL2 is a case where I'd have a hard time saying that any additional content up to the standard of the base game couldn't be anything other than worth the asking price. In 3 weeks time, it's put itself into my most-played Steam game, of all time...Sitting at ~160 hours or so.
If this first DLC drops next week as rumor says it will...I'll probably end up dropping the other $20-30 to get it. I mean hell, I spent $40 on the pre-order, which given regular price+Mechromancer would have been $70.
You ususally get 1 DLC for "free" if you buy a Season Pass (4 DLC for $40, or $30 with pass). Whether or not you think its worth it is on you. You might not even like some of the DLC that come out, and have no intention of buying them.
Next time you need me for something, just know I've more pressing things to pursue!