Popular contemporary model:

Why is conversation so easy?

Garrod S, Pickering MJ.

Trends Cogn Sci. 2004 Jan;8(1):8-11.

Toward a neural basis of interactive alignment in conversation.

Menenti L, Pickering MJ, Garrod SC.

Front Hum Neurosci. 2012 Jun 27;6:185

But see also:

Dialog as interpersonal synergy

Fusaroli R, Raczaszek-Leonardi J, Tylén K

New Ideas in Psychology 32 (2014) 147–157

Okay, so in the absence of any answers I have found that Norrick and Tannen are the sources on this. Tannen is the most interesting that summarises all that came before:

Tannen, Deborah. Talking voices: Repetition, dialogue, and imagery in conversational discourse. Cambridge University Press, 1992.

And somebody that actually did this is in Automated Discourse Analysis is Trausan-Matu et al (most notably in the CSCL paper).

Concerning the non-verbatim repetitions occuring in conversations, this might also be of interest:

Heritage, J.C. & Watson, D.R. (1979). Formulations as Conversational Objects. In G. Psathas (Ed.), Everyday Language (pp.123-162). New York, NY: Irvington Publishers.

Some possible references:

TANNEN, D.

REPETITION IN CONVERSATION

LANGUAGE 63, 3, 9-1987

1987 pp. 574-05

SANTAMARIA GARCIA, C.

SELF-REPETITION AS A FOCALITY DEVICE

AEDEAN PROCEEDINGS OF THE 17TH INTERNATIONAL CONFERENCE

2000 pp. 463-66

PERRIN, L./DESHAIES, D./PARADIS, C.

PRAGMATIC FUNCTIONS OF DIAPHORIC REPETITIONS IN CONVERSATION

JOURNAL OF PRAGMATICS 35, 12, 2003 pp. 1843-60

Lee (2012) includes a section on "repetitional responses" to y/n-questions.

Lee, S.-H. (2012) Response Design in Conversation, in The Handbook of Conversation Analysis (eds J. Sidnell and T. Stivers), John Wiley & Sons, Ltd, Chichester, UK. doi: 10.1002/9781118325001.ch20

Repetition exploited by learners:

Cekaite, Asta & Aronsson, Karin (2004) Repetition and joking in children’s second language conversations: Playful recyclings in an immersion classroom.  DiscourseStudies 6(3), 373-392.

Hi, I'd add John Du Bois's work on Dialogic Syntax, which is predicated on the ubiquity of repetition in dialogue:

Du Bois, John W. (2014). Towards a dialogic syntax. Cognitive Linguistics 25/3. 359-410.

There's also a welter of studies of "structural priming" in psycholinguistics, which studies how in dialogue we reuse and recycle our own and our conversation partner's structures:

Ferreira, Victor S. and J. Kathryn Bock (2006) The functions of structural priming. Language and Cognitive Processes 21: 1011–1029.

Pickering, Martin J. and Victor S. Ferreira (2008). Structural priming: A critical review. Psychological Bulletin 134/1: 427-459. 

Popular contemporary model:

Why is conversation so easy?

Garrod S, Pickering MJ.

Trends Cogn Sci. 2004 Jan;8(1):8-11.

Toward a neural basis of interactive alignment in conversation.

Menenti L, Pickering MJ, Garrod SC.

Front Hum Neurosci. 2012 Jun 27;6:185

But see also:

Dialog as interpersonal synergy

Fusaroli R, Raczaszek-Leonardi J, Tylén K

New Ideas in Psychology 32 (2014) 147–157

The Deborah Tannen book mentioned above, Talking Voices, is a great place to start for a comprehensive source on this. I was also going to mention Pickering & Garrod's work on Interactive Alignment, but Allen Braun beat me to it. But here is the definitive paper from BBS, as a draft on Garrod's homepage:

http://www.psy.gla.ac.uk/~simon/TOWARD%20.html

Other suggestions, also with regard to 'intensity':

Aitchinson, J. 1995. "Say, say it again Sam": The Treatment of Repetition in Linguistics. In: Fischer, A. (Ed.), pp. 15-34.

Bamford, J. 2000. You can say that again. Repetition in discourse. Clueb, Bologna.

Bazzanella, C. 1993 Dialogic repetition. In Löffler ed., Dialoganalyse IV. Atti IADA (Basilea 1992), Niemeyer Tübingen, 285-294

Bazzanella, C. 1996 (ed.) Repetition in Dialogue. Niemeyer. Tübingen

1997 Repetition in Pre-school Children's Narratives in Weigand E. (ed.) Dialogue Analysis: Units, relations and strategies beyond the sentence. Atti IADA (Bologna 1995). Niemeyer, Tübingen 29-42

Bazzanella, C. 2011 Redundancy, repetition, and intensity in discourse in Elda Weizman, Anita Fetzer (eds.) The Discourse of Redundancy, special issue, Language Sciences, 33 (2), 243-254. doi:10.1016/j.langsci.2010.10.002

Fischer, A. (Ed.) 1995. Repetition. Günter Narr Verlag, Tübingen.

Gili Fivela, B., Bazzanella, C. (Eds.) 2009. Fenomeni di intensità nell’italiano parlato. Cesati, Firenze.

Johnstone, B. (Ed.) 1991b. Repetition in discourse, vol 1. Ablex, Norwood.

Here are two more papers dealing with this topic from a dialogic syntax perspective:

Nir, Bracha , Dori-Hacohen, Gonen, and Maschler, Yael. (2014). Formulations on Israeli political talk radio: From actions and sequences to stance via dialogic resonance. Discourse Studies 16(4): 534-571.

Maschler, Yael and Nir, Bracha. (2014). Complementation in linear and dialogic syntax: The case of Hebrew divergently aligned discourse. Cognitive Linguistics 25(3): 523-557.

If an utterance is repeated, its relevance does not consist of novelty of content but of something else, implicated content, or illocutionary force. It may be an expression of interlocutor's agreement, or (ironically) disagreement, for example. Or of emphasis. Of support, surprise, competition. And so on. About relevance and the implications of what is not informative enough or relevant enough in conversation, a philosophical classic is Grice, Logic and conversation. About relevance as a cognitive principle from which we derive implications, there is Relevance Theory (since Sperber&Wilson 1986).

In the educational research literature, repetitions that suggest something the speaker said was important is called "marking".  Here is one paper (from a computational perspective) you may want to look at: L. Becker, W. Ward, S. Van Vuuren, and M. Palmer. 2011. Discuss: A dialogue move taxonomy layered over semantic representations. In IWCS 2011: The 9th International Conference on Computational Semantics, Oxford, England, January.  

I also found this paper interesting because it discussed the variety of intentions associated with semantic reformulations (a type of repetition): S. Murillo. 2008. The role of reformulation markers in academic lectures. In A.M. Hornero, M.J. Luzo ́n, and S. Murillo, editors, Corpus Linguistics: Applications for the Study of English, pages 353–364. Peter Lang AG.

Thanks all, this is really helpful advice - it is much appreciated.

You can find the publication that I wrote using some of these ideas here: https://epress.lib.uts.edu.au/journals/index.php/JLA/article/view/4265

Kelly, N., Thompson, K., & Yeoman, P. (2015). Theory-led design of instruments and representations in learning analytics: Developing a novel tool for orchestration of online collaborative learning. Journal of Learning Analytics, 2(2), 14-43.