On the "Arcana Bomb" thing, that is one of the great things about 4e. There are lots of ways to handle this. You can:
- You can just as easily page 42 it and use a fitting damage expression and downsize contingent upon effects added (down one for burst, down one for slow, etc). What is truly great is that, if there is no real gain in the action economy, you can just adlib some kind of cool X-Men like "Fastball Special" whereby (in the fiction) the Wizard pulls a small pint of Witchfire (or some other genre name) from a bandolier, says a word or two, taps it with wand and tosses it to the Monk when the Monk says "Bartender. Brew please!" The Monk then tosses it at the bad guys (burst 1 in 10, creatures, L + 3 vs Ref, 1d6 + 3 fire) and the "Arcane Bomb" explodes with the equivalent punch of a standard At-Will. No action economy gain over the monk just using a standard at-will. Just some fun, handy utility (but not overpowering) and some narrative dynamism. Win.