The question whether or not display pilots get enough practise is relevant only when the display demands skills not normally exercised by the individual. It is normally possible to put together a display sequence that will adequately demonstrate the aircraft to the public without adding manoeuvres requiring excessive practise; however, some people are not content with that and want to impress more. They therefore need to practise more.
Beagle's point about enjoying BBMF despite the fact that their displays are much more constrained and potentially less impressive than their civilian counterparts is relevant here. The flight has been able for years now to fly a very full season of displays with only a reasonable amount of practise and little fatigue on the aircraft. Long may they continue to impress without wasting people or machines.