The more airports/segments the more taxes creep up.
You have minimised UK APD by only doing a LHR-VIE stop... To reduce it totally you could do a transit through LHR and then go back by Eurostar but I suspect that would end up costing more.
Depending on when travelling (MH Malaysian is due to join oneworld shortly which would open up KUL-LHR on this ticket on MH A380). This is likely to happen in December and the oneworld fare rules will then enable MH booking.
KUL/SIN have a wealth of LCCs (Air Asia, Tiger, Jetstar) which makes it very cheap to jet around SEAsia.
If wanting to ad segments I would consider in Australia (eg Ayers Rock, Great Barrier Reef)