The base damage and the Dex increase wouldn't result in a HUGE increase to Twashtar/Rudra's Storm damage, but the increase would be there all the same. It wouldn't necessarily be something so noticeably large that you could easily just eyeball it, but if you were to have parsed yourself over a long period of time with your 85 Twashtar, and then the 90 Twashtar under the same conditions (same mobs at the same level, same buffs, etc), the 90 would come out ahead.
Lady Jinte wrote:
Vlorsutes' Negotiation Skill rises 0.2 points
Vlorsutes' Observant Parent Skill rises 0.3 points
Vlorsutes' Argument Diffusing Skill rises 0.1 points