Before you get the battle tower (when there is a force field blocking access to the elevator platform from the throne room), if you teleport to Hermaphroditus the lighting is predominantly orange, and it is difficult to see the illusionist, though you don't need to be able to see him/her to use his/her services.
There were skill trainers added in FoV to teach higher levels of skills (Lockpick, at least) ...don't recall if there were any new skills that the BF trainer couldn't teach. I assume having equivalent services in Aleroth was just to make it a complete hub, support the claim that Aleroth had grown into a prominent city, and not require trips back to the battle tower, that wasn't used for anything else (besides the storage chest).
Also, when starting a new FoV game, services in Aleroth can help if you don't care for the random BF servants.
The illusionist place is Chez Chanelle.
