Parallelomania was a term perhaps coined in 1830, coincidently (or is it?) the same year the Book of Mormon was published.
I put some  notes  together a few months ago on evaluating parallels. I would like to hear some of your methods for discerning the significance of a proposed parallel and some examples as well.

William Hamblin’s own summary of methodology:

If one wishes to discuss divergent models for the origin of the Book of Mormon, the proper methodology to be followed is: 1—Assume that the book is an authentic ancient record and analyze it from this perspective; . . . 2—Assume that the book is a nineteenth-century document and analyze it from this perspective; 3—Compare and contrast the successes, failures, and relative explanatory power of the results of these studies; 4—Attempt to discover which model is the most plausible explanation for the origin of the text

From Hamblin’s critique of Nibley:  (I am trying to put things in my own words, though)

1. Parallels should come from the right time. It doesn’t do to assume uniformity of thought and culture for a given area.
2. Parallels should come from the right place. A hemispheric region for an ancient setting is overly broad, just as a modern setting that Joseph Smith studying foreign and European literature is also overly broad.
3. Anti-parallels should not be ignored.
4. A multi-dimensional approach should be used: for example use tools from both from comparative literature and historical reconstruction.

From Brant Gardner’s review of Wirth [I am not quite as skeptical as Brant G. is about the worth of Spanish parallels]:

1. Be very cautious in the uses of secondary sources. (discern reliability of cited scholars, recognize the influence of mediating cultural layers that add distortion. Example, Spanish christianizing Mesoamerican legends.)
2. Similarity in elements is not necessarily evidence of  an indication of a historical connection. Further argumentation is required: show that paralleling elements have unique “features that would be difficult to replicate by independent invention.”
3. Do deal with anti-parallels, but be wary of using a “silly putty” classification scheme for parallels and anti-parallels. For example, having a scheme where parallels represent the original deposit of faith while anti-parallels are a result of apostasy or mistransmitted oral traditions. (Popper: “theories that explain so much and that seem to be immune to falsification ought to arouse our suspicion.”)
4. See Hamblin’s #1 above (#2 is less of a problem for Wirth (narrower area), but there are still problems with some ideas crossing over between antagonistic cultures in the same area).
5. Recognize that rhetorical skill can artificially strengthen or weaken a parallel.

From Poulsen’s review of Norman:

1. Control for “the Light is better over here” phenomenon. Recognize that more information is available for some settings than others, which increases the odds of getting false positives.