Dear Luis,
I enjoyed my 14 days in China very much, and I hope to write a comment on it to help the following travellers.

During the whole trip, Mogao Grottoes impressed me most. Personally I think the Mogao Grottoes are awesome and definitely worth seeing. The Mogao Caves are very special and definitely worth a visit if you are in Dunhuang. The art is fantastic and well preserved. Unfortunately you cannot take photos in the caves and you have to go with a guide - you cannot walk around in the caves on your own.
About the Big Wild Goose Pagoda, Around the Pagoda it is really nice and quiet, many garden ! I really like the style of the Pagoda, for once it looks old ! I wouldn't say this is an essential sight to visit. But since you're already in Xi'An, there isn't much else to do. Similar buildings can be seen all across China. It's the same with all other Xi'An sights apart from Terracotta warrior. And there were also many interesting places in Xinjiang, which you cannot miss.
I have to say you did a good job, and congratulations.
Regards,
Ross James Clark
Austrilia