Hi, well I have the LX5 predecessor the LX3. I also have the K100 (6mp) and K20 (14.6 mp). I also shoot landscapes, cityscapes - things that don't move (often). I picked up the LX3 about 2 years ago for business trips, where I just could not take a SLR with me. In that respect it is a wonderful camera. I like it a lot.
All of that said, comparing the LX3 or 5 for that matter (essentially the same sensor) and a dSLR be it the K100 or K20, is really an apples and oranges exercise. The largest difference I see is sensor size which directly translates into noise, especially in the evening. I do have to say it does as well as it can (which is really pretty good), however it is very difficult to compete with a much larger sensor, especially at ISO 400 and 800, and forget anything above that. The K100 and K20 do well up through ISO 1600 and I have had good luck at ISO 3200 ( with post processing noise reduction).
Size wise obviously the KX 3/5 wins hands down. I really love the Leica f2 lens. It is great, and does very well. Again, as I said, its a wonderful camera for what it is, however you are trying to compare two completely classes of cameras.
Here are some LX3 images....
The lenses on the Pentax, is a hard one, especially if size is a consideration. The 12-24 is a wonderful lens (I have it and use it a lot). It large drawback it - well, its large, no doubt about it. That said, its like shooting with a number of primes - its that good. I also have the FA31 Ltd, and I really like it. I use it for stitched landscapes, due to its sharpness.
Actually, to compete with the LX5, I would go with the KX and DA*15 and DA*40, if you desire the best in image quality. 2 very small and light lenses, that would pack well, would be excellent for landscapes and general use (the 40 is less than an inch thick - I believe). However, the Pentax DA 18-55 is a very small kit lens that will also do very well - I would not count that option out at all (see the kit lens thread in the lens area). I would also get a very small and light travel tripod and external shutter release. In this way, you can trade f stops for longer shutter speeds coupled with higher ISO speeds. You will be able to get wonderful ambient low light landscapes with long shutter speeds, with excellent image quality and better resolution.
Now you can do the same with the LX5 (tripod and external release) using the manual controls and lower ISO speeds in order to reduce the noise, and still come out with great images.
Bottom line - Pentax will be a bit larger (but the lenses are actually very small), vs the LX5 where the entire unit will almost fit in a pocket - well a jacket pocket.
Hope that helps...