It can be enlightening, but the only real thing it illuminates is the wavering nature of Hitchcock's muse: a collection of songs that "didn't fit in with what I was doing at the time [=the first three albums] and do fit in with each other now"; how successful this combination actually is remains debatable.
Mostly it consists of traditional blues (sometimes not even imaginatively titled: Blues in A), bordering on pure goofing off; few tracks salvageable at the idea level (the opener All I Wanna Do Is Fall in Love).
Invisible Hits by the Soft Boys was a whole album released late, Invisible Hitchcock is a collection of leftovers, and Robyn Hitchcock's leftovers are predictably embarrassingly poor in quality.