Improving my kit - help!

So, in an earlier topic I asked what lens to buy for a trip to Australia. Almost everyone recommended purchasing an UWA. If I decide on an UWA, it will be the Canon 10-22mm, because of the great things I've read about it.

Anyway, I decided to get more into photography, ie building a new kit. This isn't necessarily for a trip to Australia, just to get more into photography. You can guess, I need your advise.

To begin, here's what I enjoy shooting:

• Landscapes
  
• Architecture
  
• Tennis (not much lately, though)
  
• Everyday things, ie 20-80mm range

You might wonder what is wrong with my current setup. 95% of the photos I shot this/last year were with my 17-70mm, most of them in the 17-30mm region. Here's the main problem with this lens, I'm not sure if this is due to the lens itself, the body, or this problem is just unavoidable.

When there is enough light - the lens performs quite well. Sharpness is okay from f/4-5.6 (I prefer f/5.6 and f/8 most, though), contrast is quite good (just a little levels needed in PS). However, when it gets dark, quite some detail is lost and I am often disappointed. I know photography is all about light, I just wish it performed a little better in situations where light is not optimal.

For bettering my kit, I have decided to spend about 1000EUR, maybe 1300EUR if I sell both of my lenses (17-70 and 70-300). I've been reading a lot lately and came up with the following options:

- Keep the Sigma 17-70mm, buy a Canon 10-22mm (-450EUR) and Sigma 30mm (-350EUR). Cost: about 800EUR.

This option would get me an UWA and a Sigma 30mm. I like the Sigma 30mm because of its (sharpness at) f/1.4.


- Sell the Sigma 17-70mm (+200), buy a Canon 10-22mm (-450EUR), buy a Tamron 28-75mm (-300EUR). Cost: about 550EUR.

This option would get me an UWA and standard zoom with f/2.8. Downside is switching between the lenses.


- Sell the Sigma 17-70mm (+200), buy a Canon 17-55mm (-630EUR), buy a Canon 85mm f/1.8 (-250EUR) / Canon 70-200mm f/4 (-400EUR). Cost: about 680-830EUR.

This would get me a Canon 17-55mm, of which I have read nothing but positive things. However, it is a little short at 55mm, so maybe a 85mm f/1.8 would be an option. I don't shoot portraits though - it's just for the extra reach. For this reason, I'm not sure if the 85mm would be a great option.


- Sell the Sigma 17-70mm (+200), buy a Canon 10-22mm (-450EUR), buy a Canon 24-105L (-760EUR). Cost: about 1000EUR.

I like the idea of the 24-105L, however, it is f/4 so I'm not sure if this would really be an improvement. I have read things of users claiming it isn't as sharp as they want it to be.


Two more things:

I'm not sure about purchasing an UWA. It might be put to good use for trips to Australia, NYC, London and such, but I am actually wondering if this lens would actually be used not on trips. I'm not sure if I would call it a 'specialty' lens but it does come close, doesn't it? Moreover, I sometimes, but certainly not all the time, find 17mm restriciting a shot a pano. Most of them worked out just fine - I have an amazing pano of the view from Sentinel Dome at Yosemite, shot without a tripod.

Basically, I'm trying to build a kit which performs great when there is enough light, but also good to great, when there light conditions are not optimal. Please note that I'm not referring to concerts/bars, just when the sun starts setting / when it is cloudy. For example: I was in NYC last Christmas and after about 4PM, it was getting dark. The lack of detail in shots became quite visible in PS/Lightroom.

If there is an option which isn't listed above, please let me know!

Anyone?

I have some examples of what I find unacceptable. I do understand that lightning was average to bad in some pictures, but is there anything I can do about this? The images look pretty dull to me.

All shot with my 300D, 17-70 @ 17mm. f/8, ISO 400, 100% crops. Shot in RAW, but playing with exposure in Lightroom didn't really improve the lack of detail.