I used to work in a Holiday Village who took Sun Holidaymakers. At this place, Searles of Hunstanton, the levels of service and accommodation were exactly the same as those offered to full price guests (very high). Cut price holidays were offered off peak to fill the site and maintain site usage.
The only downside as far as the staff were concerned was that having paid a very reduced rate for their holiday many (not all) people expected reduced price in the restaurant and bar too. The prices, when I worked there, were in keeping with local pubs and restaurants but that wasn't good enough - they'd come away for a cheap holiday. Oh how we laughed!
Watch out for the small print though, it's only �9 per person if a certain number of people (usually 6) are sharing. Great value for a family - lousy for a single parent like me.
If you do decide to go, check with the parks concerned exactly what is supplied, a lot of them offer very limited facilities with additional top up charges. Searles, at that time, did not (don't know if that's changed).
Yes, the family who own the site are friends of mine but I'm not that biased!!