balanced are they worth it?

One thing not stated here is the equipment, meaning, are you using the XLR cables on equipment that has been designed as a balanced circuit? It is my experience (with my Amp, DAC, and Tuner) that some equipment sounds better with XLR because of its circuitry. You should consider this as well. It often is the reason why short XLR runs (.5m or 1m, not just long runs, will sound better. Good luck!

If the gear is truly balanced then you null out the second harmonic using balanced cables, but little of the gear with balanced connectors is truly balanced. Given a clean ground single ended wires will perform as well as balanced wires in the bulk of the cases.....Clean ground is the rub.....

2 things that have been mentioned are important: the length needs to be over 2 meters (probably 3) for you to hear a difference. This is true, unless the equipment you are using has a fully balanced topology within it (as Mento refers to). If that is the case, then balanced will almost always sound better. Another issue which has not been mentioned is the environment. If you live in an area with alot of RFI and EMI, balanced will make a substantial improvement by just canceling out the noise that is picked up from these sources. This occurs because the 2 hot leads are out of phase. It of course does not eliminate all of the EMI/RFI noise, but it does reduce it significantly.

What I have done in the past is contacted the manufacturers of the equipment and asked them their opinions.

I recently changed from unbalanced to balanced, 3 months ago, and I've been pleased. I would say overall, the noise floor is definitly lower. The instruments come from a blacker, darker background, if you will. The strange thing I've noticed though, is that I have a harder time telling the difference between cables. For example, the difference between XLO Reference and Signature seems much more pronounced to me unbalanced then in the balanced form. Maybe I'm crazy (my wife won't disagree) but I prefer the balanced form overall. Gotta go , Dickie Betts is jamming, man this sh@t sounds good.