Although BMI is disappearing or at least is going to have a new parent sometime next year, it can make sense to buy some Diamond Club miles if you have planned use for them in the next six months or so.
If you have not bought any miles this year, you can buy up to 16K miles that after 50% bonus will become the maximum 24K that can be bought during a calendar year. Of course you can have other family members to buy miles as well…. The price of 24K miles is 207 GBP.
There are still few gems left of the redemption side. One of my favorites is the Zone 2 to Zone 10 i.e. from Morocco to Maldives via Europe. When you book this as two one ways, you can have stop overs for example in Bangkok on outbound and Singapore inbound. You can book this for only 30K Diamond Club miles + 210 GBP cash component for return flight in business. You need to pay the actual taxes and fuel surcharges that will be on the high side.
As I pointed out earlier, the BMI Diamond Club is probably going to cease exist sometime next year. The current owner of BMI, Lufthansa, has made an agreement with IAG, the parent of British Airways and Iberia, for selling the airline.