Thanks again for the pointers. I have some good news and some bad news....

The good news is that I managed to convert the ImportPointFile scripts to import multiple polylines from a single CSV file (1 polyline per data row).
This works well and the resulting curves simply require 2 joining lines - one along each end - to produce something that can be networked into a surface.

The bad news is that MOI struggles badly with networking the area I'm working on - in fact it never completes the job.
The area is approx. 2400m x 2400m with data sampled every 1m. That results in 2400 polylines, each line with 2400 data points.
That means we're connecting close to 6 million data points. I'm sure I could resample it but I need that level of detail I'm afraid.

Can anyone advise on a way forward please or suggest an affordable modelling package that might handle that kind of landscape size?
It's frustrating as I thought I was almost there. MOI is an incredible piece of software and I use it for all my modelling now. It's got to be the most well thought out modelling package out there but I suspect I'm pushing the boundaries here.

Thanks