"Specialised gearing" that's a nice diplomatic phrase, I would use a rather more colourful phrase to describe Brompton's gearing options My advice after owning an SRAM 6 speed Brompton and having ridden a BWR 6 speed is "just don't do it". After having researched a whole load of other options I did a Nexus 8 / Double chainring conversion on our Bromptons which gives a gear range of 18.5 - 82 gear inches. This is about perfect for us and our touring and daily usage (Norway not being know for its flatness). The Nexus hubs are 'cheap as chips' so if something goes wrong you can replace the hub without breaking the bank. We're quite pleased with the conversion (caveats apply).

If I am to modify the Bromptons again then it will be to fit Rohloff hubs in them. We have them in our touring bikes and they are brilliant.

You are right about the Brompton's foldability and that you can roll the bike on its rear rack when folded. This is a useful feature when taking the bike on a train or a bus.

The big problem is that you take an already expensive bike, spend time fitting more parts that cost more money and maybe you end up with a bike that suits you. That sort of sums up modifying a Brompton.