The arts (and some other phenomena) come in two basic types which affect the imagination differently.
Some of the arts are like an alternative, virtual reality - they take the mind and draw it through an experience of stimuli and emotions. For example, cinema is of this type - the movie-goer is taken-into the world of the movie and moved-through the experiences.
Other arts of this type include theatre and opera, and most primitively the narrative song.
Such an experience does not allow, is not intended to allow, much space or scope for self-awareness or freedom - the ideal is an immersion in the sub-world of the art.
But there are other kinds of art which allow space for the participant to become self-aware, aware of his own agency - these arts demand the use of imagination.
For example, the written poem - which historically was abstracted from a performed song, has a quite different effect on the imagination; relying far more on the reader than does the song on the listener. The written poem may be delayed, paused, re-read in part or in whole, in written sequence or any other sequence...
It seems that Shakespeare only became recognized as a great imaginative poetic writer (in the eighteenth century) when his plays were printed and read (indeed, the translation into German seems to have been a vital step in his recognition); this greatness was (presumably) not apparent when the plays were seen only in performance, because the audience were simply drawn-into the play, and experienced it as an alternative world in real time.
The novel, invented by Samuel Richardson with Pamela in the middle eighteenth century - was a major technical breakthrough in stimulating sustained activity of the imagination. On the one hand the novel provides considerable structure and guidance for the reader, on the other hand there is a necessity for the reader to provide a great deal from his imagination (e.g. character and setting visualizations, the 'acting' of the participants, much of the motivation and emotional responses).
In sum, the novel could be summarized as a play or movie that has been 'realized' by the novel-reader - who must take on roles of producer, actors, director, scene painter, costumier, editor etc.
Furthermore, compared with a play, the novel reader is in world 'out of time'; the play-watcher is necessarily drawn-through the play at the rate and pace of the performance - his mind filled throughout; but the novel reader proceeds at whatever pace he feels - and may pause or break away for any period, think and imagine, and then resume.
Some music provides scope for imagination, space for the autonomous mind to know itself; but other music - especially songs and operas - take-over the mind, and draw it through a particular sequence, and at a set pace.
So, listening to instrumental music by JS Bach may provide a context for self-awareness of the autonomous soul; while attendance at Das Rhinegold by Wagner at Bayreuth would hope to be an immersive and overwhelming experience, a living of the world being depicted.
Some music (Debussy and Delius spring to mind) is very obviously designed as a background-tapestry for contemplation (or, in a more debased fashion, as mood or ambient music.) But other music is designed to overwhelm us, to control us, to compel us to recapitulate a fixed linear experience - outwith of vocal music, this was more a feature of later classical music, such as the 'late romantic' symphonies of Mahler or Bruckner or Tone Poems of Richard Strauss.
This distinction applies to some church services as well. (Bearing in mind that some church services are not intended to be emotional or imaginative experiences, but function at a much more low key and matter-of-fact level.)
Some services take the participant through a particular set sequence of experiences and emotions which (more or less) 'fill the mind'. A successful Anglican liturgy is more or less of this type - and the effect of great language (from the Book of Common Prayer and the Authorized Version of the Bible)can be emotionally as overwhelming as any opera or symphony. But there is not much space for the imagination - nor is there intended to be.
At the other extreme was an experience of a full-on Greek Orthodox service on the island of Tinos back in 1978. I could not understand the language, and the meaning of the service was seen only in the very slow changes of visual theme (also, I was not a Christian then). But the service provided a backdrop or 'tapestry' of consisting of sonorous male-vice chanting, rich clothing and objects, ritual movement and music...
I experienced this as a sustaining context for a high level of awareness and the knowledge of freedom, with scope for the free imagination to work-within.
Another way to think of this is that some (but not all) arts have (when they are working properly) the ability to wake us up!
It is this feeling of 'coming-to' in the world - when we have previously been 'asleep' or non-conscious.
This can be regarded as an emergence of the real self, coming out from behind the false/ phony/ social/ mass media or 'robot' self of trained/ instinctive/ automatic responses.
The activation of the imagination (the real self) is certainly not confined to 'arts' - but can (and indeed should) be a feature of philosophy (in the board sense of the word - also including theology).
Real philosophy is of this type - and this explains why real philosophy is something that happens essentially in solitude, during reflection - not in company, not during teaching, and only seldom during discussion (when attention is usually grabbed, and the mind is usually filled, by the social context).
My thesis here is that:
1. There is a need for stimulation of the imagination, because adult modern man is nearly always starting from a situation of alienation - and imagination is the destined cure.
2. Imagination needs structure, but it also need space.
3. Overwhelming experiences, immersive experiences (drama, movies, TV, etc)... these may be mistaken for imagination-stimulating, but they essentially keep-out the imagination. This is important! because sometimes they feel like imagination; and in a sense they are... but this is somebody else's imagination!
3. Imagination is more often about reading (in solitude), and landscape, and brooding-meditation and the like; in a nutshell, imagination is usually a start-stop business.