Sertorius and Spartacus both fight a little better. After Spartacus nips Crassus' army in the bud, Pompey is recalled when the gladiators are again able to run wild in Italy. Spartacus manages to keep his less strategically inclined generals in check and fights his way over the Alps before Pompey arrives. Mithridates sees what is going on and throws a party all over the Eastern provinces like it was 88 all over again.
Rome effectively loses its empire by the mid 60s. Sertorius is considered an enemy even as he offers assistance from his based in Spain. The Roman political class still decides to fight for power even as they fear an invasion of Italy from three sides: Spain, the gladiators in Gaul and Germania, and Mithridates new confederacy in the East. Roman control of Italy collapses and the city of Rome shrinks back into a moderate power as it cannot import mass quantities of grain anymore.
Flash forward 2000 years and outside of the Spanish Republic (which may not be a republic and may be even less connected to its Roman founding than say Constantinople of 1453), no one really considers Rome to be anything more than one more upstart Hellenistic imperial minded city.