I still don't own an RBA, but I've pretty much always rebuilt my coils for my T3's. The fact that it was even possible was a selling point for me. It was partially for saving money, but more just because I like to mess with things. The heads are what, ~4 bucks a piece (I'm considering shipping for a handful of them?) And they last around a month without you having to really mess with them aside from the occasional cleaning. In the grand scheme of things it's not much of a value difference, though cheesecloth and kanthal do allow me to have fresh heads for pennies a piece. It's exponentially cheaper, sure, but it was cheap to begin with, you know?
I will say that I like the performance of the coils I built myself a little better. I wind them to a slightly lower resistance and this combined with the cheesecloth makes for what I think is an all-around better vape than I get with stock heads. The stock heads are good when they work, but they seem to have problems. They're just a tad quirky. The ones I rebuilt not only give me a better vape, but do so flawlessly. I just feel like you only get your money's worth in terms of performance and reliability if you rebuild them. I guess I just have more confidence in the coils I build myself. Plus, if I get a bad one (which does happen,) it doesn't have to go to waste. I can just rebuild it to get it up and running.