Dawn is a science mission producing fantastic results. ARM is political masturbation. ARM is another example of government dysfunction.
Electric Propulsion is great for long duration missions like Dawn and for station keeping. But chemical propulsion is how we currently get to orbit so the marginal cost to go a bit farther is not much greater (F9 gets 13 ton to earth orbit for $60m. FH gets the same mass to mars orbit for $120m. Add to that the cost of the 13 ton payload... [a craft with a payload of its own] means the cost of a $60m craft to mars orbit is only about 50% more than to LEO.)
Where EP could be very useful is to recover a humans to mars orbit transporter for reuse which also serves as emergency backup thrust.