All good points you guys make. For me, the deadly hazard for low level flight is that the consequence of one mistake (which you can recover from at height) may kill you at low level. Many, many very good pilots have died while flying at low level. Sure, training lessens the risk compared to not training, but avoiding it lessens it a whole lot more (for me anyway).
Flying in balance/rudder control, bank angle, steep turns at low speed, loss of horizon etc are all things we should be practicing, and I do. However I can practice most of those things flying tailwheel and aerobatics above 3000 ft. Flight around the right sort of cloud below 3000ft is also great for co-ordination. Formation training also sharpens a lot of skills. If there is a genuine need for low flying, go for it. If you are a non professional pilot and want the skills associated with it with reduced risk, I think there are other ways where the consequences of a mistake may not be so deadly.
One other thing springs to mind. Is there a restriction on taking passengers when low level? I think non pilot passengers are probably unaware of the risk and should not be taken, just as you should not have passengers (other than instructors) when practicing emergencies. Cheers.