Of course, it's not only about definitions and terminology, but in this essay, Pauline Hogeweg, who coined the term 'bioinformatics' in 1978 or 1980 or as early even as 1970, describes what her group initially used the term for: "study of informatic processes in biotic systems".
Informatics or informatic processes are actually pointing at the 'flow of information through a living cell, individual, species or evolution'. Hogewegs' work is focused on pattern recognition, morphogenesis and evolution.
In other words, bioinformatics covers a very broad range of topics and originally wasn't even meant for sequence based , or even hard data-driven research.
So metabolomics easily fits in this definition, as long as you study samples from a 'biotic' origin. Reasoning that (small) metabolites have an important role in information transfer is obvious, certainly in drugs discovery.
Does this make you a happier bioinformatician?
I hope not. (as your own opinion and feeling is what matters in the first place)
Is this answer placing metabolomics right at the heart of the bioinformatics community?
I think not, but the good news is that after having sequenced 'everything' in 2012 or 2013, and some chewing on this in the years after that, bioinformaticians will have to follow 'experimentalists' to the core discipline of biology metabolomics is to become sooner or later.
Since you asked for citations to primary literature, I recently came across this article: Earliest pages of bioinformatics.