I don't mind the vibrations, but the few rattles I cannot get rid of is what has me tempted.

I'm assuming the urethane side mounts will do their job to keep the rear mount from having trouble and hoping with a rubber rear mount most of the shock felt in the car would be less severe.

 

solid mounts are good. but you cant deny the rattle, and clutch chatter. ive used hasport mounts in various cars. some of the cars were tolerable, others unbearable. the worst - eg civic with h22 engine and no balance shafts. this car rattled so hard that alternator mounting bolts would snap.

a good solution for me has been to mix up the mounts like you suggested. ive had good success with a solid rear mount and rubber side mounts, or the other way around with solid side mounts and a rubber rear. the engine of course becomes less stiff but its a decent trade off between performance and comfort.