The OP asks
"Are people you've often disagreed with politically still good people? Can they be seen as having good motives even when you disagree with their politics?"
I would hope so and I would hope that most rational people could feel that way too.
It is very difficult to leave behind your knowledge of a politician and talk about his/her personality away from the political arena. I think you can only go on an instinct/gut feeling as to your perception of another human being and for the most part we, the people, can only ever get to see our politicians through the media, which has an opportunity to
try and mould an image of our politicians according to it's particular persuasion/political entrenchment .
As for the media entrenchment it has to be accepted that if you only read a newspaper you believe wholeheartedly gives you the only truthful information you need, only agree with the t.v programs that suit your own political view then you become somewhat brain washed albeit voluntarily. Likewise any voter that states they would never vote for any other party, engages heavily in activism to my mind will not 'for the most part' shift away from taking the obliged party line. You see and hear that in interviews or comments from the latter group as there is often a mantra, a repeat of the exact same words, the sound bite, propaganda. The definition of 'Spin' after all is ensuring that others interpret an event from a particular point of view.
It is very hard to look past all these vested interest groups/parties but I think most people have woken up a bit to the 'subliminal' message they try to bombard us with and do accept that behind every politician there is a human being. If anybody thinks one party is saintlier than another, one party has more humorous characters than another, one party has kinder souls than another , one party is devoid of having it's good, the bad and the ugly then they are deluding themselves.
There has to be a dividing line for our politicians between their political persuasion and their personality away from the job. Yes I can disagree with someone's political view but still think they he/she is a good person. Likewise I believe a politician can have good motives even if I don't agree with them. If I didn't then I would be a tad worried about my own sanity.