Hey Zoom,
There's a couple of ways to balance out the sky with the foreground. My preferred method is to use a graduated neutral density filter to restrict light on the top half of the frame without darkening the bottom. You can also shoot the scene deliberately dark, maintianing detail in the sky and then bringing up the detail in the fore-ground in post-processing (see my comments below about contrast/histogram). Lastly, you could shoot several shots from a tripod so they're all the same framing. Shoot one to expose the shadows only, one to properly expose the sky only and one or more at intervals in-between them. Keep the aperture the same and adjust shutter speed. Blend the exposures in photoshop (some labour required) or a program designed to do HDR (select the group of images, sit back & sip coffee or other drink of your choice, then admire/tweak the results once the blending is finished.
If I don't have a filter with me or I can't use it, I turn the contrast all the way down in-camera and will shoot the scene making sure I don't blow the highlights. However, you have to make sure you don't under-expose the image too much. If you're in this position, you need to use the histogram when you review your shots and not the actual results on the LCD. You have to make sure that your histogram is as close to the right without going over....in fact you probably want the bulk of the histogram to the right. Shadows in the photo can generally be recovered this way (with minimal noise hopefully) and your highlights remain in tact. Whatever you do, don't blow the highlights because once they're gone, they're gone. shadows can always be recovered.
The spot that appears in your sunset shot also appears in a few other photos. I suspect your lens is fine and that you've got dust on your sensor. This is pretty easy to correct in most cases by simply blowing the spot off (with a blower, not by blowing). If that fails, there's a whole bunch of sensor cleaners out there which range in price from pretty cheap to pretty expensive. One of the tricks I used (though I don't recommend it per se) is to get scotch tape (not the clear stuff, but the 'milky' tape) and lay it across the sensor and then remove it. It's not strong enough to damage the sensor, but it will get all the dust. That said, I don't really recommend this as over time it could leave a residue. Currently, I'm using a product called dust-aid. It works very well and is about mid-range as far as price goes. I've used it several times including in the field (again, not really recommended) to get rid of dust spots that screwed up a couple of images.
For the purple lines around subjects, I think you're referring to purple-fringing (I didn't see any in your photos though). Unfortunately, when you've got a sky on the verge of blowing out and dark lines, you're pretty much going to get fringing (depending on the lens I get purple or green) The easiest method I know of to remove that is in any form of photoshop (and probably most other programs), using the hue & saturation, select the dropper tool and click on a part of the fringing. Then desaturate it & if needed, adjust hue so it matches the background. Keep in mind, I've pretty much stopped using photoshop so my recollection could be a bit off on the exact steps.