I have close ties with Mazda...according to the techs there the problem with busting engine mounts doesn't lie with the sp23 but with the MPS model. No upgrade was done on the engine mounts of the MPS they basically used the same ones as the NA Sp23. there lies your problem.
I have driven a SP23 as my brother in law is looking at also buying one of them...very nice car if I do say so myself.
I havea 1.8 SRI Astra H and would have bught a SP23 over the astra IMHO they are that good.