Whether or not it would be a good idea depends a lot on your specific school as well as your future plans. Most schools have very strict engineering requirements in order to have ABET accreditation, while physics is typically much more lenient. My school has a 4 year EE/Physics double major where the tech electives for the physics BS are filled completely with the EE classes. Therefore, you're able to take ONLY the core physics classes (mechanics, E&M, thermo, quantum, etc). This option would be awesome for someone who wants to end up in an EE grad program because they will already be prepared for quantum mechanics etc, and they will not loose any engineering electives (only tack on additional physics classes). On the other hand, if you're aiming for grad school in physics, then this double major would probably be a poor choice because you'll only have the basics and no course work in any particular sub field of physics. It all really depends on where you want to end up...
For me, I'll probably just do physics and take some EE electives which will allow me to go to physics or EE for grad school. I'll be much more restricted in EE grad programs but I'm only interested in the more physics oriented EE topics anyway.
As for becoming a quant... I have no idea really but I would think that physics/math or physics/finance(?) would be a better option than physics/EE. And that's only if you REALLY just can't see yourself not doing physics, otherwise, I would say just do math or finance.