I didn´t cross checked how accurate the stated drop stacks from the various sources are, but mlb Drop CEs yield more Currency per spent AP until reaching a breakpoint that is +4 for silver currency if the Event planer is accurate for the single currency stage (i assume they accounted the fact that the boss / miniboss drops a huge chunk of the stacks and are unaffected by spawn bonus). After that running 100% spawn bonus and 2 MLB CEs is better than running 3 MLB CEs for silver currency. Probably for the other currency the same.

That´s for single currency nodes.

For mixed nodes spawn rate is pretty sure always better, since the MLB drop CE only account for a part of the drops.

Considering the fact that the mat drop rate however increases dramatically with spawn boost, i would say spawn boost is more worth.