So, MB seems to be a contentious issue...

How about the number of fans earned for a victory depends on the level of MB used (plus the additional cash requirement)?

To illustrate here are a few examples using the 0%-50% MB slide scale:
1. If you use 0% MB and win, you will gain 200 fans for a 142k+ stadium and 1000 fans for 142k and less stadium
2. If you use 25% MB and win, you will gain 100 fans for a 142k+ stadium and 500 fans for 142k and less stadium
3. If you use 50% MB and win you will gain zero fans
4. If you lose your game your fans will decrease as it does at the moment.

That way the rankings will be more heavily weighted towards teams that don't use MB.

what happens if you already have 154k fans then use 50% MB

Sorry Phantom, not a great idea, as a lot of the teams in the top level use max mb despite what they say. So unless you use mb you will always lose. The point being unless you use mb you can't win as everyone is too afraid to lose by not using it.

Maybe the effect of MB should wear off, as it would in real-life. Or limit it to 5 times a season.

In the first version of Rugby Manager, you'd have 30 lots of steroids to give your players each week (I think). They'd last 24 hours. So, for example, you could give all 15 players a boost, only 2 days per week.