My personal opinion about the light effect for the golden outfit is Cipsoft just trying to make the outfit more attractive for the buyers. 1kkk for an outfit is insane to me but hey they are a business so they do whats best for them, but as of today theres only like 30~ players with the outfit.
The light effect is still a nice touch, although I believe the majority of Tibia players dont even play with light effects anymore... Also there are mounts like the Blazebringer & Crystal wolf that gives out a light source aswell :D
What i'd much rather see is Cipsoft making every mount more unique, there was a proposal long ago by a player wanting to make every mount have a unique ability. Like the draptor have +5% fire resist when you are mounted, or maybe some mounts increase your skill by +1 etc..
That would be really interesting and make collecting mounts and using them so much better :D