Witnesses get paid 1 Steem (I believe in Steem Power)

Correct! :) For the top19, this amounts to about 1370 SP per day.

they also are a part of the discussions to determine what changes are and are not pushed through

This is not really true; the witnesses can be overridden by the steemit account if necessary. This already happened during the hardfork to recover from a steemit.com exploit stealing user keys.

One final note here is that there was a change in a recent fork where a portion of Steem Dollars on payouts were instead given as Steem, which I believe was used to bring the SD/USD ratio within acceptable ranges.

This was actually done to reduce the ratio of SBD to Market Cap, as I refer to as the "debt load" of SBD. Essentialy, a SBD is an 'IOU 1$ of STEEM', and if there is too many of these IOU's, the economy can crash. So, we pay out less IOU's until the economy has time to recover (by people executing the IOU, or the steem market cap increasing.) I discussed this a bit along with my price feed decision in my latest witness update.

Regarding whom to vote for: another important question to ask is, "What are you doing with 1370 Steem Power (current value 520$) per day?"