Some interesting ideas...
Sunder is a good way to scare the PCs a lot. Their cool new toys, Nooooo! But remember that only a item of equal plus can sunder a magical weapon. So if sunder efforts fail, and the bad guy gets slept or held or something, they end up with more stuff. Unless you use an Evil or Exotic weapon.... Evil seems cheesy, exotic is much more interesting. On the other hand a mithril or adamantium weapon can be used - not actually magical, but has the enhancement bonus. And if the PCs survive, they end up with their opponents weapon - not magical, and potentially even better than what they have now, but it will take some work and effort to improve the mithril or adm. Could have the built in slow- down affect.
regarding the Escape idea - can be cool, but capturing the party is always very tricky. You really need to either get them into a situation where they surrender willingly, or through several encounters at them, each with an increasing chance of a successful capture. Poison is the best bet - with some magical aid for hold persons/sleep/charm spells to get those with better fort saves. After the second attempt, they will be running scared. If they continue to defeat every attempt - give them a chance to run a scam on the bad guys - 'fake' their own capture or somesuch - a few party members captured, the rest holding the best gear, ready to track them, find the lair/origin of the goons who keep trying to capture them, etc. Hmm, I'm growing increasingly fond of this idea. Wonder if I can adapt it to my own game....