As a guide Mrs T and I recently did BRU-LHR-DXB/HKG-LHR-BRU. we started our trip by going out on Eurostar to BRU, return fare £69.00 each (yes VK we had a reality check!). Our first weekend two night in the Hilton EUR300.00 in breakfast plus meal in hotel. Our “return trip from BRU, accomodation at Hilton again EUR74.50 including breakfast.
Our total cost was around £550.00, but we did have one full weekend in Brussels and a night, but on our Club World/Europe fares we save just over £2500, so we are still nearly £2K better off and a nice weekend in BRU. We could have taken the BRU bit in a day and saved the accomodation costs.
If you have the time its a great way to save and have a weekend away, but also you get another 80 tier points and if BA Gold or Silver another 2500 miles.