I agree, I found the ‘Friends Leaderboard’ to be an awesome motivator. Although, In my personal opinion, I don’t know if filtering by membership level would be quite as effective. For me, it was a greater motivation to see users clocking up a regular 20k a day when I was only able to kick in 5-10k a day, gave me that little extra motivation and a point to set my goals. Also you may have seen some users achieve well above their membership level cap and a few Breaker users that rarely finish a day over a couple of thousand steps.
Only my personal thoughts on the possible drawbacks.