Mathers - CAT III is not worth installing. If you look at the small number of diverts CWL experiences every year - and therefore lost revenue - installing CAT III would have a payback period of about 20 years!! The ILS upgrade would cost next to nothing - but the associated runway lighting would be extremely expensive - do the sums by boy, not worth the installation cost.
Besides, look at the number of diverts which CWL picks up from BRS - more than outweighs the number of flights it loses.
As for the horse about putting off new operators, simply not the case. Airline / airport discussions consider all options and if an airline was prepared to sign up to an agreement to operate from CWL, then the management would be prepared to upgrade the system. Not rocket science!