I have to agree with Art here. Yes, he has been thrown in and out of the team, but that's his job at the end of the day. He may be a natural winger, but of course he won't be getting any games there. He was a decent winger because of his workrate and effort in tracking back; not because of his ability. Now that his engine is going though, he really won't have anything more to offer for us at the highest level.
Some may find it disloyal, but football can be a brutal business at times. You cannot afford to hang onto players for too long due to sentimentality. In fact, I think we're being kinder to him if we sell him during the summer, because it means he'll actually get to play football next season, as opposed to simply staying here and sitting in the reserves. Look at what happened to Berbatov. A lot felt that he was a waste this season and that if we weren't going to play him, then he should have just been moved on. I think that it's the same for Park really. He's been a good servant, but he won't feature, so why keep him hanging around? It doesn't make a lot of sense to me.