Is there a significant performance difference between Truecrypt encrypted drives using only AES vs disks that use a triple algorithm scheme like AES-Twofish-Serpent?
The Twofish and Serpent stages will significantly reduce performance, compared to simply using AES alone, as the data must pass through three encryption algorithms rather than just one. This difference is magnified if your processor supports the AES instruction set, which accelerates AES encryption and decryption in hardware.
You generally don't need the additional security provided by triple encryption unless the data truly are extremely critical. If you follow best practices, such as using a sufficiently long and complex password, there should be no security concerns using one of the encryption algorithms alone. AES is computationally infeasible to crack, and likely will remain so in the foreseeable future; this is even more so with Serpent and Twofish.
See also: Which TrueCrypt Algorithm is the safest?