Hi Helen.
I live right by the park and can tell you that you'll only experience queues on Bank Holidays etc. Then you'll find queues for about 5 miles to the north of Kidderminster.
If you are coming during a holiday period then I'd advise reaching the park via Stourport. You come into it the back way then with something like a nine mile detour around Kidderminster.
Inside the park I believe it all runs pretty smoothly. I haven't been there in years.
Have you been watching the documentaries about the park on ITV Central (Sunday's) then. You may get them a different day in your area, wherever that may be.
http://www.wmsp.co.uk/index.php
http://www.wmsp.co.uk/home_safaritv.php
wherever that may be.
Just seen the Welsh flag so you must be coming from Wales then.