I hate to be a parrot, but: excellent post.
When I first got back into judo (and first started taking BJJ) I was exactly as you described - I loved going against the guys I knew I could beat; I hated going against the guys I knew could beat me. Luckily I realized fairly early on that, doing this, I wasn't really getting much better, whereas the guys I was throwing/tapping a month ago were all of a sudden giving me a good fight.
Lately I've made a point of asking our instructor to spar a round or two after every class, and they've been gracious enough to oblige. I get completely clowned every time, but every time I take something away from it.