Even the Aussies had a choice and the chose to keep her as head of state! So let's have one big referenda to choose the way the UK should go...
Sovereign or republic
EU or not EU
Currency euro or pound
One big happy UK with one parliament making decisions on behalf of the whole UK or separate parliaments (or school assembly for the Welsh) including separate treasuries, border controls and defence.
One final point, for now, if (when) we did become a republic we'd only get the same sorry-arsed politicians running for el presidento we have now, and maybe the odd 'celebrity'. At least with the royal family you know what you're getting into, and spending - how much would security cost just for previous el presidentes every few years? Smile, it could be worse