I definitely agree with buffalo--surprise visits are not the best idea just because so many things can change last minute and its a lot of money to spend to not be able to see your cadet. Roughly every other weekend is a training weekend, meaning most of Saturday will be used up (and no leaving on a pass). And at any time, restrictions can come down on a squadron or even the whole wing, and even those with plans might have them cancelled. The military really doesn't care about plans, I know of cadets who had approved plans to fly home for a long weekend and had to cancel them at the last minute for whatever reason.
If you plan a visit ahead of time, your son/daughter will need to put in paperwork that (if approved) will allow him/her to leave the hill and stay with you in a hotel for the weekend (after LMD on Friday generally). If worse comes to worse and you fly to COS and your cadet can't leave, you can meet at the Chapel wall and spend time talking. Its great to visit, and both my husband and I flew out at separate times to do that, but we planned it ahead of time and it worked out fine! Even though it wasn't a surprise, our cadet was still thrilled to see us! As were the friends that came with us to dinner etc.! They love to get away for a bit, especially that doolie year.