I always figured "overmining" was an excuse for conducting subspace weapons tests on Praxis, which explains partly why it exploded the way it did (subspace shockwave event) and the ban on such weapons on the Kithomer Accords afterwards.
The Narada event happening on their doorstep probably had the Klingons stepping up their production/testing. With similar results it would seem.
Exactly. The "Nero event" kicked off something of an arms race in the JJ-timeline, so both the Feds and KDF stepped up their game. So as you said, the KDF just caused Praxis to explode sooner than it would have otherwise.