Seminarians should be identifiable in their role, particularly at liturgies the question though is how best to achieve this.
In my seminary, as for Facite, we do not wear cassocks but do dress formally for special occasions (including liturgies). The difficulty I have with cassocks, aside from the cost, is that they can become something which a person can hide behind, allowing them to present an “other self” to those that they meet. This would obviously be reduced if cassocks were only worn for liturgical occasions. That said, the limited amount of use would make it difficult to justify the cost. As well, seminarians also need to be identifiable as such outside of liturgical events but a cassock is not the most practical garment… As far as I know, there are no seminaries in the UK which wear cassocks and only one in Australia.
Ultimately, like collars and priests, wearing (or not wearing) a cassock isn’t what makes a seminarian who they are. If you want to know how healthy a seminary is, don’t look at what their students are wearing but at how they relate to and treat each other.