It'll be more a case of being able to find trainers willing to teach new skills for a price, or manuals with information on new potions and traps for Henrietta, and other similar gear, rather than upgrading equipment.

Having said that, the mercs should be aware that certain rare metals could give an advantage in a fight, such as silverite being poison to darkspawn, dragon leather being fire resistant and so on. Such things may have an impact on the roleplay if a character managed to get himself (or herself) enough dragon leather to get a whole suit made so they could walk through flames unharmed.

Should take a fully grown high dragon to get enough material for a male character, and a baby dragonling for a female one. :P

Wouldn't Cassius like a sabre which would burn darkspawn on contact?