Read for references about salamanders and junk-DNA:
C.Cristofre Martin & Richard Gordon, 1995
Differentiation trees, a junk DNA molecular clock, and the evolution
of neoteny in salamanders.
J. Evol. Biol. 8: 339-354
It's highly speculative, but it gives a nice view: by losing the ability
to metamorphose, the DNA coding for adult features gets the possibility
to mutate and duplicate without any constraints = this is the reason for having
a large amount of (junk)DNA.
Although your thoughts sound likely at first side, I think it's less likely to
chance junkDNA in something usefull and functional again then to chance a just
duplicated or mutated gene into something usefull in living creatures and
gives them the possibility to be favoured in a new environment.
Coline van Moorsel
University of Leiden