Coming from someone who has owned Solo HDs, Tours, Studios, and iBeats, I would say the in ear ones are not worth it, period, and that its better to invest in the over the ear, for two reasons.
One, I usually use in ear headphones for casual use, in the gym, anywhere where I just stuff them in my picket after using them. So I don't really take care of them at all, and the headphone plug is usually the thing that breaks. The plug on the Beats is nothing special, the actual speakers are. So with that in mind, I broke my Tours 3 months in twice, and now awaiting the warranty ones to come in so I can sell them new. I prefer $20 JVC Marshmellow headphones since again, I don't use in ears for anything special. And if they break, just go and buy another pair, nothing to freak out about. Great sound too, and very light.
Now for the on ear ones, Solo HDs and Studios, I've listened to plain Solos and for the extra $30, the quality is definitely noticeable. The Solos just are a bass house, while the Solo HDs are a lot more balanced and have better sound. The Studios are better, clearly, and offer real notice cancellation that actually works. The only downside, is the constant use of batteries. I hated that. I prefer my Solo HDs to the Studios mainly because of that. Now, if the cable on the Solos/Studios breaks, I can simply get another for $5-15, depending the the brand since its just a 3.5 mm to 3.5 mm, nothing proprietary or fancy.
In the end, using White Solo HDs and loving every second. Hope this helps.
Sent from someone's Galaxy Nexus running AOKP + Franco