There are no cost reductions to run witness nodes as yet. Over time the costs have simply grown, though to some extent this was expected. The MIRA version (with its associated cost reductions) isn't recommended for witnesses.

I don't think the witness reward mechanism is perfect, but if we are looking narrowly at the reward amount, I think the analysis that was done when it was reduced by 80% and set to 10% of total inflation was reasonable and hasn't changed significantly, therefore the split shouldn't change. Proposals to revamp the system in a more fundamental way can be considered. I'm open to looking at it.