I have had my runners,broad beans and onions in the same beds for 3 years now and have always done very well,mind you,I always dig in new green manure and I use bone meal or fish blood and bone as a top up if need be,you cannot beat the stuff!
I always allow the old beans/vegetation to rot back into the soil.plant different flowers or another veg in amongst the rows of my onions which seems to work for me anyhow.
I do change tata's ,though last year I grew the majority in dustbins and such.