I had decided (99.9%) to buy resale before I took my DVC tour and I NEVER felt like I was wasting the guide's time at all. I had many reasons for taking the tour: 1) I had never been to SSR and was considering it as a possible home resort 2) I wanted to tour the model for Aulani and get more info about that resort since I hope to use my points there every few years and 3) Since I had done plenty of research ahead of time I wasn't at all concerned my guide would convince me to change my mind and buy direct. However, to be 100% sure (instead of 99.9% sure) that resale was the way to go I personally needed to take the tour. It was a piece of mind thing for me. If I'm going to spend 10s of thousands of dollars on something, I don't want any doubts. Also, I let them know ahead of time that I was considering resale AND that I wasn't going to buy anything on that day. And my guide was great. He never tried to mislead me in any way. In fact, after discussing things for a few minutes he agreed resale was the best choice for me. He also then asked me to listen to the reasons why I sould consider direct. All of them were legitimate, but like many resale buyers just not important to me.
So if you want to take the tour, go for it. Just make sure you are prepared.