First, when you buy the new expansion, you get a level boost to 90 for free. You only need to buy it separately if you want multiple characters at 90.
Secondly, being good with your class is now only required for Flex level raids and higher. You can see all of the game without knowing how to play your character. Blizzard has at times re-introduced minor difficulty in 5-mans (heroic 5-mans at the start of Cataclysm, Icecrown 5-mans) but while some people liked that, most of the players didn't.
Thirdly, you say you'd be "mad to pay" $60. I could easily see myself having $60 worth of fun trying out another character class. What other things can you buy for $60? You can easily spend more just eating out in a good restaurant, and that'll give you only two hours of fun.