Why not add a new equipment slot to both standard and town clothes that creates a small visual effect in the air around the character. It doesn’t add any stats, or radiate to any real degree, and doesn’t clash with legendaries, which add a visual effect set on the character.
These could be purchased via the cash shop for 25 gems, and four could be forged together in the mystic forge to create a more pronounced version of it, up to several ranks.
Visual effects are also not visible to enemy players in WvW, or usable in sPvP, to prevent any form of imbalance.
As a basic idea, one version could create a small multi-colored sparkle in the air around the character. Another could create a minor snowfall. And a third could make a mild heat blur around the character.