OK, I've got my mesh. π The original cad contours had 1.3 million edges.
Thanks guys for your suggestions... like I said - it's been a great learning experience.
TIG - I experimented more with the simply contour plugin - most of the problem were with my contour set - some were ludicrously convoluted whereas most were quite simple. There was no one setting that did a good job with all of them, but with some selective processing of different sets of contours based on complexity, it worked well.
Ogan - I tried tgi3d amorph. Haven't had time to explore it all properly (hardly at all actually - there seems a lot too it), but I ran through your suggested method. I had a similar experience here to that described above. Setting a 20m segment length worked for some of the contours, whereas other lengths were required to get anything acceptable for other segments. In other words I had to do a lot of selective processing using different settings to get a good overall result.
In the end I used "Edge Tools" to simplify all the curves to within 2m of the original, then went and cleaned up the overlapping contours with reference to the original dwg. At the same time I deleted any extraneous noise. This all took about 1hr, but wasn't too onerous. Then I just used the sandbox tools to create a mesh from contours. The result is shown in the attached. This was definitely the quickest way to process the entire contour set in 1 go and came up with an acceptable result. I think my method posted at the beginning of this thread gave a really nice result, but was too labour intensive for anyone dealing with a lot of lines, but otherwise I'd recommend it.
mesh.jpg
thanks again for your help with this...
Regards
Mick