Taking into account an extra year, you will be saving creditors some 4 years 0f admin and costs, by the time everything happens, so I feel that an offer of £10k is a reasonable one. Of course, it is impossible to second guess creditors !
In the long run, if the arrangement continues to run, you get to keep 50% of any pay rises, so they are not all lost, and, of course, they outlive the IVA as well.
As regards the marker on the files. Yes, it is easier to get finance with the IVA showing but marked as completed, but not by a lot. The real improvement comes when the marker falls off at the 6 year mark and the world opens up again.
My opinions are merely that .. opinions based on experience. Always seek professional advice.
IVA Completed 23rd July 2013 .... C.C. 10th January 2014