I would not pay to level up an alt... but if I were to start on a new server? I actually might.
Starting out on a new server, even with heirlooms you still end up sometimes strapped for cash.
Boosting up to 90 so you have a 'money-runner' so to speak might be worth it.
Personally I've leveled up probably 30 characters since I started playing shortly after launch in EU.. I find it enjoyable compared to a lot of other time-wasters. Sometimes I just want to mindlessly derp around after a long day of figuring shit out at work.
I doubt I will make use of it, but I can see situations where I could.
Especially with the amusing exchange rate/cost of living difference between the US and where I live... 60 bucks is roughly 4 pints :p