When to buy WOTLK

Well, I was wondering, I have TBC as part of Battle Chest and now my little hunter is at 35, and I was wondering, are there any content improvements for the levels 1-70 included in WOTLK that aren't really minor? I was thinking to buy WOTLK at level 55 in order to make a death knight, but I thought you guys would know more. Help?|||Wait until 55 if you want to make a DK right away... I'd honestly completely suggest staying away from DK's until you're at least 70. Buy WotLK at 66 or so (Give it a day to go through, basically, just in case... I know some people have had to wait like up to 2 days or so to get their WotLK order online to go through.)

Really, wait until you're a higher level and have done some dungeons. Possibly even make your DK a tank if you want to truly experience it in dungeons so you can really fully feel the class out, because otherwise you might get some bad "omg, another DK, we'll see how crap they are" because a lot of people are experiencing the "Hero class = Most popular, and now a bunch of noobs play it" syndrome.|||Here is it is in a nutshell (hopefully I didn't mess up any of my numbers.)

<55: Wrath gives you no benifit.

55: Wrath lets you make DKs

60: Cataclysm (which requires Wrath) will allow you to fly in the old world*

65: Wrath lets you access the Northrend JC, Cooking, and Fishing dailies. It also lets you train your professions to 450.

68: Wrath lets you got to Northrend

70: You can't level any further without Wrath

*This isn't really a big deal, as you can fly in Outland at 60 with just BC, and that's where you'll be leveling.