I love the heirlooms, as stated above, it makes me feel somewhat good when i run around with my mw german and lordly heraldic mail with tabard, withstanding quite some arrows/hits, even tho i do not run around in the armor all the time, i enjoyed creating it.
Trying out new specs without the need to create new char is also sexy, i am usually retiring to try new spec/tweak out the one i play the most so it could fit my playstyle the most. And having an item improved in the process is just the cherry on top of a pie.