Hi Leigh!
You have some very good questions there. I will answer a few of them out of order.
Firstly Mars. Mars is well past opposition (which is the best time for viewing it) as a result it is very small. Of all the outer planets, Mars is the one that has the greatest variability in its apparent size during its cycle. At a good opposition it is easy to pick out the ice caps and other features even at only moderate magnification. But right at the moment it is small and as it gets lower in the evening sky atmospherics affect it more.
Saturn. The Cassini division is the large gap in the rings and should be capable of being seen at moderate power given reasonable atmospheric conditions. Again as it gets lower in the west these become harder to see. The bands on Saturn are very subtle. Filters can help a bit to increase the contrast but they will still be subtle. It is also well past opposition now so it is a small target.
The good news on planets is that Jupiter is approaching opposition, a few months to go, I think the actual date is mid Febuarary 2015, bit its will become more prominent as the months tick by.
Alpha Centauri. Anywhere over 100x should be sufficient to separate the A and B components of Alpha Centauri. Again it is fairly low in the evening sky so poor atmosphere can make this harder. As for the flairs. All bright stars will display some degree this. If it is even around the star its is not collimation related. Poor collimation effects on the image are often poorly understood. A poorly collimated newtonian will have stars in the centre of the field displaying some degree of coma. Note the collimation doesn't cause the coma, only cause it to be visible in the centre of the field. This guide to collimation has quite a good sample of optical issues at the bottom of the document
http://www.astro-baby.com/collimatio...on%20guide.htm . You willl note that coma exhibits as stars appearing as little comets.
Malcolm