blimey TC, Hope you aren't as abrasive to work with in the cockpit!
Of course things were looked at in great detail when the original ASU's were set up. Each county had its own research to do with regards to their geography and demography, but I would say that air support is one of the few areas in policing where the wheel hasn't been reinvented 43 times - you only have to look at the narrow choice of aircraft types that exist - not much beyond the 135 and 902, is there, save for a few still clattering round in 355's and of course Dyfed. The situation wasn't a million miles from the " hey, lets all buy twins" scenario you describe. Singles have been tried at points in time ( Lancs had a 47 for a while, Strathclyde a 206, amongst others) but they were found wanting and so things evolved into highly capable, superbly equipped, twin engined machines.
What the Police hasn't historically been good at (and I concede it isn't the only thing!) is moving dynamically with the times. We now have a "model" for police aviation, bolstered by the PAOM and because of that you will see very little innovation and willingness to revisit things to see if, at this moment or that moment in time, our needs have changed. This has been particularly the case in the police use of firearms, where only very gradual evolution was taking place until a rewrite of the guidance manual and study of less lethal options (which had been around for decades) has led to a major rething in the ways operations are conducted.
I haven't - at any time or elsewhere - decried the efforts of ASU's in this thread and you were a little offside in suggesting that I had.
My point is - can you imagine where military aviation would be now if the willingness to revisit and expand concepts had not been prevalant. The likes of the AH64 and Mil 24 would never have been invented. In fixed wing terms, who would ever have thought that we would be taking out cars in deserts with missiles dropped from Predators? The latter example probably better demonstrates the low cost option.
Digital mapping is now coming to the forefront. The IOM police has access to aerial hi res pictures of the whole island, and I understand that a number of UK forces also utilise this. Another low cost option, negating the need for a photographic sortie. However, such a sortie could quite comfortably be carried out by a light single, or - to push my point - even a microlight. This would actually be quite a bit more covert, as there isn't a great deal of other people who hover around in twin engine helo's, where there is a lot who burn around the skies in robbos and gossamer winged lawnmowers.
Indeed, have a look at what Steadicopter is doing
http://www.steadicopter.com/
The game is up TC. Don't forget the job is run by beancounters and a spotty, playstation generation probationer can now replace a multimillion pound ASU with a laptop and a toy helo. The new turbine ones even make the right noise! That puts an extra ten bobbies back on foot patrol, the hangar can be sold for low cost housing cos the 'ASU' is now in the back of a transit van, and the pilots can be released back into the staff- strapped aviation market! Someone could get promoted on the back of this idea.
Before you go off on one again Thos, please read all of this with tongue firmly in cheek
Bottom line - ASU's do a great job, but we must constantly look at what is going on. If I was a ground commander at a riot and had the option of launching an expendable model helo at tuppence an hour, or an EC 135 at a cost per hour far in excess, I know which I would choose. The final aviation solution for the policing of the British Isles has not yet been arrived at.