program.cs

using System;
using System.Collections.Generic;
using System.Diagnostics;
using Newtonsoft.Json;
using System.Reflection;
using System.Collections;

namespace ConsoleApplication25
{
    class Program
    {
        public class SourceInnerData
        {
            public int Id { get; set; }
            public string Data { get; set; }
            public string ExtraData { get; set; }
        }

        public class Source
        {
            public int Id { get; set; }
            public string Name { get; set; }
            public string ExtraData { get; set; }
            public ICollection<SourceInnerData> InnerData { get; set; }
        }

        public class DestInnerData
        {
            public int Id { get; set; }
            public string Data { get; set; }
        }

        public class Destination
        {
            public int Id { get; set; }
            public string Name { get; set; }
            public List<DestInnerData> InnerData { get; set; }
        }

        static void Main(string[] args)
        {
            var c = new Copier();
            var src = new Source() { Id = 1, Name = "TestSource", ExtraData = "Blah", InnerData = new List<SourceInnerData>() { new SourceInnerData() { Id = 2, Data = "Inner Data" } } };
            Stopwatch sw = new Stopwatch();
            sw.Start();
            for (int i = 0; i < 1000000; i++)
            {
                var dest = c.SerializeCopy<Destination>(src);
            }
            sw.Stop();
            Console.WriteLine("Serialize elapsed: {0}", sw.Elapsed);

            sw.Restart();
            for (int i = 0; i < 1000000; i++)
            {
                var refl = c.ReflectionCopy<Destination>(src);
            }
            sw.Stop();
            Console.WriteLine("Reflection elapsed: {0}", sw.Elapsed);
        }

        public class Copier
        {
            public TDest ReflectionCopy<TDest>(object srcVal)
                where TDest : class, new()
            {
                if (srcVal == null) { return null; }
                TDest dest = new TDest();
                var props = srcVal.GetType().GetProperties();
                foreach (PropertyInfo p in props)
                {
                    PropertyInfo objPf = typeof(TDest).GetProperty(p.Name);
                    if (objPf != null)
                    {
                        if (objPf.PropertyType.IsGenericType && typeof(IEnumerable).IsAssignableFrom(objPf.PropertyType))
                        {
                            var destCollType = objPf.PropertyType.GenericTypeArguments[0];
                            var recurse = this.GetType().GetMethod("ReflectionCopy").MakeGenericMethod(destCollType);                            
                            IEnumerable srcList = (IEnumerable)p.GetValue(srcVal);
                            IList destlst = (IList)Activator.CreateInstance(objPf.PropertyType);
                            foreach(var srcListVal in srcList)
                            {
                                var destLstVal = recurse.Invoke(this, new object[1] { srcListVal });
                                destlst.Add(destLstVal);
                            }
                            objPf.SetValue(dest, destlst);
                            continue;
                        }

                        if (p.PropertyType == objPf.PropertyType)
                        {
                            objPf.SetValue(dest, p.GetValue(srcVal));
                        }
                    }
                }
                return dest;
            }

            public TDest SerializeCopy<TDest>(object srcVal)
                where TDest : class, new()
            {
                if (srcVal == null) { return null; }
                var temp = JsonConvert.SerializeObject(srcVal);
                return JsonConvert.DeserializeObject<TDest>(temp);
            }
        }
    }
}