having experimented for several hours and knowing an absolute i.e that my router/firewall/java settings were fine before LW stopped connecting, I've finally got it up and running again BUT I'm sure that the above solution only applies in situations where the cache hasn't been updated for quite some time (as Farj3R says) and it is definitely rewritten each time the app is started which means inserting a new cache url may be unnecessary.

I personally found that increasing the locale preferencing setting finally did the trick - still unsure why but was always convinced that a preferences file was corrupted somewhere within the .limewire folder