The reasons are listed here:
http://www.insolvencyhelpline.co.uk/ccj ... easons.htm
I think the problem will be by including it in your IVA will be deemed an admission.
The CCJ does have an impact on your credit score but so do defaults, an IVA flag and poor payments so overall getting it removed wont have to much impact.
The one area where is does have an impact is re-mortgaging as CCJ's are still considered when underwriting mortgages and can effect rate.
At present mortgage lenders look at CCJ + Value whereas there is a move towards simply counting the number of CCJ's over a given period and ignoring the value.
To give you an idea with an IVA flag you would need more than 5 CCJ's for it to have a small increase on a mortgage rate. (Based on underwriting criteria at the top 5 sub-prime mortgage lenders)