The A380 wake issues should be mitigated in the future with RECAT, and of course even today there is no wake separation required between a pair of A380s, which is not the case for two Heavies on approach: So the benefits of A380 ops will increase if a critical mass is there, even if just over a period of ten minutes or so.
Where did this 1% of LHR traffic figure come from? It's more like 3.5% at the moment, which is a lot more significant.