If you buy the K10D, your just gona hate yourself when you see the K20D's price drop (Because we all know, eventually sometime next year, it will - just as the K100D and the K10D's did.)
Id go for the lens, and probably the sigma, due to the price.

My local family owned photography shop stocked pentax
then they got taken over by wilkinson cameras (chain store) and they dont stock pentax, nor second hand equiptment, and the guys workin there arent nearly as knowledgable!

Maybe your attempt at selling as stock photos isnt working, because these simply arent the types of images people want to use - most of your stuff is, well, i dunno, just not what you would use as stock I guess - the images are nice, very nice, just not the kinda thing thats used as stock

try looking through stock sites and basically start off copying ideas, and then develop them, and by that time, you should be able to create your own, and
sell some stock

I dunno, that was a pretty poor attempt at a suggestion, since I myself know very little about stock photography.

Yeah that way is the best way if you have a tripod If not, then you can just use one RAW, and alter the exposure in your RAW converter. It gives lower quality results if your original image is more underexposed or overexposed (because detail is lost) but otherwise it seems to be okay

I use Photomatix Pro, any idea whether Artizen is better?

Example of my technique using Photomatix:
http://img265.imageshack.us/img265/7774/flyinggrassstainsbydeepja1.jpg

and i found a tutorial on this technique if you're interested]
http://www.gfxvoid.com/forums/showthread.php?t=26130

If you take pictures in RAW - an uncompressed format (PEF on pentax cameras, and also DNG on the K10D I think) then in photoshop, or a RAW converter, you are able to "change" the exposure of the picture (basically, alter the brightness of it) and thus save 3 or 5 versions of the same image, with different exposures, to combining to HDR. This is different from taking one shot in JPEG format and changing the brightness and combining to HDR because in a RAW format image, a lot more information is stored, however they do take up alot more room on your memory card

Id personally use RAW format than 5 seperate shots, but thats just personal preference, it also means that you dont need a tripod
Is the quality better with bracketted shots merged to hdr?

The only filters that do anything that you can't do in photoshop are polarizers, ND filters, IR filters, and I guess, some "special effects" (like turning every light you see in the picture into a star etc, though I dont know why you would want that).

Well I think its quite interesting, although long exposures on water elements usually have stationary parts to the photo as well, the range of colors provides a nice variety in the photo

Not sure how you all will react to this but yeah,
It was both a practise of self portraiture, and post processing, aiming to achieve two different moods, and in the second shot, taking out the blemishes and spots etc.

K100D, 50mm F/1.4 (at 1.4), 1/125, Post Processed in Photoshop CS2.

Oh, and I hardly look anything like this.

So basically, to solve your problem, go on the menu and alter the value for the "Flash Exp. Comp." to 1.0